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Allergies

Allergies

Definition

Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances.

Description

Allergies are among the most common of medical disorders. It is estimated that 60 million Americans, or more than one in every five people, suffer from some form of allergy, with similar proportions throughout much of the rest of the world. Allergy is the single largest reason for school absence and is a major source of lost productivity in the workplace.

An allergy is a type of immune reaction. Normally, the immune system responds to foreign microorganisms or particles by producing specific proteins called antibodies. These antibodies are capable of binding to identifying molecules, or antigens, on the foreign particle. This reaction between antibody and antigen sets off a series of chemical reactions designed to protect the body from infection. Sometimes, this same series of reactions is triggered by harmless, everyday substances such as pollen, dust, and animal danders. When this occurs, an allergy develops against the offending substance (an allergen.)

Mast cells, one of the major players in allergic reactions, capture and display a particular type of antibody, called immunoglobulin type E (IgE) that binds to allergens. Inside mast cells are small chemical-filled packets called granules. Granules contain a variety of potent chemicals, including histamine.

Immunologists separate allergic reactions into two main types: immediate hypersensitivity reactions, which are predominantly mast cell-mediated and occur within minutes of contact with allergen; and delayed hypersensitivity reactions, mediated by T cells (a type of white blood cells) and occurring hours to days after exposure.

Inhaled or ingested allergens usually cause immediate hypersensitivity reactions. Allergens bind to IgE antibodies on the surface of mast cells, which spill the contents of their granules out onto neighboring cells, including blood vessels and nerve cells. Histamine binds to the surfaces of these other cells through special proteins called histamine receptors. Interaction of histamine with receptors on blood vessels causes increased leakiness, leading to the fluid collection, swelling and increased redness. Histamine also stimulates pain receptors, making tissue more sensitive and irritable. Symptoms last from one to several hours following contact.

In the upper airways and eyes, immediate hyper-sensitivity reactions cause the runny nose and itchy, bloodshot eyes typical of allergic rhinitis. In the gastrointestinal tract, these reactions lead to swelling and irritation of the intestinal lining, which causes the cramping and diarrhea typical of food allergy. Allergens that enter the circulation may cause hives, angioedema, anaphylaxis, or atopic dermatitis.

Allergens on the skin usually cause delayed hypersensitivity reaction. Roving T cells contact the allergen, setting in motion a more prolonged immune response. This type of allergic response may develop over several days following contact with the allergen, and symptoms may persist for a week or more.

Causes and symptoms

Allergens enter the body through four main routes: the airways, the skin, the gastrointestinal tract, and the circulatory system.

  • Airborne allergens cause the sneezing, runny nose, and itchy, bloodshot eyes of hay fever (allergic rhinitis ). Airborne allergens can also affect the lining of the lungs, causing asthma, or conjunctivitis (pink eye). Exposure to cockroach allergens has been associated with the development of asthma. Airborne allergens from household pets are another common source of environmental exposure.
  • Allergens in food can cause itching and swelling of the lips and throat, cramps, and diarrhea. When absorbed into the bloodstream, they may cause hives (urticaria) or more severe reactions involving recurrent, non-inflammatory swelling of the skin, mucous membranes, organs, and brain (angioedema). Some food allergens may cause anaphylaxis, a potentially life-threatening condition marked by tissue swelling, airway constriction, and drop in blood pressure. Allergies to foods such as cow's milk, eggs, nuts, fish, and legumes (peanuts and soybeans) are common. Allergies to fruits and vegetables may also occur.
  • In contact with the skin, allergens can cause reddening, itching, and blistering, called contact dermatitis. Skin reactions can also occur from allergens introduced through the airways or gastrointestinal tract. This type of reaction is known as atopic dermatitis. Dermatitis may arise from an allergic response (such as from poison ivy), or exposure to an irritant causing nonimmune damage to skin cells (such as soap, cold, and chemical agents).
  • Injection of allergens, from insect bites and stings or drug administration, can introduce allergens directly into the circulation, where they may cause system-wide responses (including anaphylaxis), as well as the local ones of swelling and irritation at the injection site.

KEY TERMS

Allergen A substance that provokes an allergic response.

Allergic rhinitis Inflammation of the mucous membranes of the nose and eyes in response to an allergen.

Anaphylaxis Increased sensitivity caused by previous exposure to an allergen that can result in blood vessel dilation and smooth muscle contraction. Anaphylaxis can result in sharp blood pressure drops and difficulty breathing.

Angioedema Severe non-inflammatory swelling of the skin, organs, and brain that can also be accompanied by fever and muscle pain.

Antibody A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.

Antigen A foreign protein to which the body reacts by making antibodies.

Asthma A lung condition in which the airways become narrow due to smooth muscle contraction, causing wheezing, coughing, and shortness of breath.

Atopic dermatitis Infection of the skin as a result of exposure to airborne or food allergens.

Conjunctivitis Inflammation of the thin lining of the eye called the conjunctiva.

Contact dermatitis Inflammation of the skin as a result of contact with a substance.

Delayed hypersensitivity reactions Allergic reactions mediated by T cells that occur hours to days after exposure.

Granules Small packets of reactive chemicals stored within cells.

Histamine A chemical released by mast cells that activates pain receptors and causes cells to become leaky.

Immune hypersensitivity reaction Allergic reactions that are mediated by mast cells and occur within minutes of allergen contact.

Mast cells A type of immune system cell that is found in the lining of the nasal passages and eyelids, displays a type of antibody called immunoglobulin type E (IgE) on its cell surface, and participates in the allergic response by releasing histamine from intracellular granules.

T cells Immune system cells or more specifically, white blood cells, that stimulate cells to create and release antibodies.

People with allergies are not equally sensitive to all allergens. Some may have severe allergic rhinitis but no food allergies, for instance, or be extremely sensitive to nuts but not to any other food. Allergies may get worse over time. For example, childhood rag-weed allergy may progress to year-round dust and pollen allergy. On the other hand, a person may lose allergic sensitivity. Infant or childhood atopic dermatitis disappears in almost all people. More commonly, what seems to be loss of sensitivity is instead a reduced exposure to allergens or an increased tolerance for the same level of symptoms.

While allergy to specific allergens is not inherited, the likelihood of developing some type of allergy seems to be, at least for many people. If neither parent has allergies, the chances of a child developing allergy is approximately 10-20%; if one parent has allergies, it is 30-50%; and if both have allergies, it is 40-75%. One source of this genetic predisposition is in the ability to produce higher levels of IgE in response to allergens. Those who produce more IgE will develop a stronger allergic sensitivity.

COMMON ALLERGENS. The most common air-borne allergens are the following:

  • plant pollens
  • animal fur and dander
  • body parts from house mites (microscopic creatures found in all houses)
  • house dust
  • mold spores
  • cigarette smoke
  • solvents
  • cleaners

Common food allergens include the following:

The following types of drugs commonly cause allergic reactions:

  • penicillin or other antibiotics
  • flu vaccines
  • tetanus toxoid vaccine
  • gamma globulin

Common causes of contact dermatitis include the following:

  • poison ivy, oak, and sumac
  • nickel or nickel alloys
  • latex

Insects and other arthropods whose bites or stings typically cause allergy include the following:

  • bees, wasps, and hornets
  • mosquitoes
  • fleas
  • scabies

Symptoms depend on the specific type of allergic reaction. Allergic rhinitis is characterized by an itchy, runny nose, often with a scratchy or irritated throat due to post-nasal drip. Inflammation of the thin membrane covering the eye (allergic conjunctivitis ) causes redness, irritation, and increased tearing in the eyes. Asthma causes wheezing, coughing, and shortness of breath. Symptoms of food allergies depend on the tissues most sensitive to the allergen and whether the allergen was spread systemically by the circulatory system. Gastrointestinal symptoms may include swelling and tingling in the lips, tongue, palate or throat; nausea; cramping; diarrhea; and gas. Contact dermatitis is marked by reddened, itchy, weepy skin blisters, and an eczema that is slow to heal. It sometimes has a characteritic man-made pattern, such as a glove allergy with clear demarkation on the hands, wrist, and arms where the gloves are worn, or on the earlobes by wearing earrings.

Whole body or systemic reactions may occur from any type of allergen, but are more common following ingestion or injection of an allergen. Skin reactions include the raised, reddened, and itchy patches called hives that characteristically blanch with pressure and resolve within twenty-four hours. A deeper and more extensive skin reaction, involving more extensive fluid collection and pain, is called angioedema. This usually occurs on the extremities, fingers, toes, and parts of the head, neck, and face. Anaphylaxis is marked by airway constriction, blood pressure drop, widespread tissue swelling, heart rhythm abnormalities, and in some cases, loss of consciousness. Other syptoms may include, dizziness, weakness, seizures, coughing, flushing, or cramping. The symptoms may begin within five minutes after exposure to the allergen up to one hour or more later. Mast cells in the tissues and basophils in the blood release mediators that give rise to the clinical symptoms of this IgE-mediated hypersensitivity reaction. Commonly, this is associated with allergies to medications, foods, and insect venoms. In some individuals, anaphylaxis can occur with exercise, plasma exchange, hemodialysis, reaction to insulin, contrast media used in certain types of medical tests, and rarely during the administration of local anesthetics.

Diagnosis

Allergies can often be diagnosed by a careful medical history, matching the onset of symptoms to the exposure to possible allergens. Allergy is suspected if the symptoms presented are characteristic of an allergic reaction and this occurs repeatedly upon exposure to the suspected allergen. Allergy tests can be used to identify potential allergens, but these must be supported by eveidence of allergic responses in the patient's clinical history.

Skin tests

Skin tests are performed by administering a tiny dose of the suspected allergen by pricking, scratching, puncturing or injecting the skin. The allergen is applied to the skin as an auqeous extract, usually on the back, forearms, or top of the thighs. Once in the skin, the allergen may produce a classic immune wheal and flare response (a skin lesion with a raised, white, compressible area surrounded by a red flare). The tests usually begin with prick tests or patch tests that expose the skin to small amounts of allergen to observe the response. A positive reaction will occur on the skin even if the allergen is at levels normally encountered in food or in the airways. Reactions are usually evaluated approximately fifteen minutes after exposure. Intradermal skin tests involved injection of the allergen into the dermis of the skin. These tests are more sensitive and are used for allergies associated with risk of death, such as allergies to antibiotics.

Allergen-Specific IgE Measurement

Tests that measure allergen-specific IgE antibodies generally follow a basic method. The allergen is bound to a solid support, either in the form of a cellulose sponge, microtiter plate, or paper disk. The patient's serum is prepared from a blood sample and is incubated with the solid phase. If allergen specific IgE antibodies are present, they will bind to the solid phase and be retained there when the rest of the serum is washed away. Next, an labeled antibody against the IgE is added and will bind to any IgE on the solid phase. The excess is washed away and the levels of IgE are determined. The commonly used RAST test (radio allergo sorbent test) employed radio-labeled Anti-IgE antibodies. Updated methods now incorporate the use of enyzme-labeled antibodies in ELISA assays (enzyme-linked immunosorbent assays).

Total Serum IgE

The total level of IgE in the serum is commonly measured with a two-site immunometric assay. Some research indicates that there is a higher level of total serum IgE in allergic as compared to non-allergic people. However, this may not always be the case as there is considerable overlap between the two groups. This test is useful for the diagnosis of allergic fungal sinusitis and bronchopulmonary aspergillosis. Other conditions that are not allergic in nature may give rise to higher IgE levels such as smoking, AIDS, infection with parasites, and IgE myeloma.

Provocation tests

These tests involve the administration of allergen to elicit an immune response. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Delayed allergic contact dermatitis diagnosis involves similar methods by application of a skin patch with allergen to induce an allergic skin reaction. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount of the test substance administered as an opaque capsule along with a placebo control. Provocation tests are not used if anaphylaxis is is a concern due to the patient's medical history.

Future diagnostic methods

Attempts have been made for direct measurement of immune mediators such as histamine, eosinophil cationic protein (ECP), and mast cell tryptase. Another, somewhat controversial,test is electrodermal testing or electro-acupuncture allergy testing. This test has been used in Europe and is under investigation in the United States, though not approved by the Food and Drug Administration. An electric potential is applied to the skin, the allergen presented, and the electrical resistance observed for changes. This method has not been verified.

Treatment

Avoiding allergens is the first line of defense to reduce the possibility of an allergic attack. It is helpful to avoid environmental irritants such as tobacco smoke, perfumes, household cleaning agents, paints, glues, air fresheners, and potpourri. Nitrogen dioxide from poorly vented gas stoves, woodburning stoves, and artificial fireplaces has also been linked to poor asthma control. Dust mite control is particularly important in the bedroom areas by use of allergen-impermeable covers on mattress and pillows, frequent washing of bedding in hot water, and removal of items that collect dust such as stuffed toys. Mold growth may be reduced by lowering indoor humidity, repair of house foundations to reduce indoor leaks and seepage, and installing exhaust systems to ventilate areas where steam is generated such as the bathroom or kitchen. Allergic individuals should avoid pet allergens such as saliva, body excretions, pelts, urine, or feces. For those who insist on keeping a pet, restriction of the animal's activity to certain areas of the home may be beneficial.

Complete environmental control is often difficult to accomplish, hence therapuetic interventions may become necessary. A large number of prescription and over-the-counter drugs are available for treatment of immediate hypersensitivity reactions. Most of these work by decreasing the ability of histamine to provoke symptoms. Other drugs counteract the effects of histamine by stimulating other systems or reducing immune responses in general.

Antihistamines

Antihistamines block the histamine receptors on nasal tissue, decreasing the effect of histamine released by mast cells. They may be used after symptoms appear, though they may be even more effective when used preventively, before symptoms appear. Antihistamines help reduce sneezing, itching, and rhinorrhea. A wide variety of antihistamines are available.

Older, first generation antihistamines often produce drowsiness as a major side effect, as well as dry mouth, tachycardia, blurred vision, constipation, and lower the threshold for seizures. These medications also have similar effects to a alcohol and care should be taken when operating motor vehicles, as individuals may not be aware that they are impaired. Such anti-histamines include the following:

  • diphenhydramine (Benadryl and generics)
  • chlorpheniramine (Chlor-trimeton and generics)
  • brompheniramine (Dimetane and generics)
  • clemastine (Tavist and generics)

Newer antihistamines that do not cause drowsiness or pass the blood-brain barrier are available by prescription and include the following:

  • loratidine (Claritin)
  • cetirizine (Zyrtec)
  • fexofenadine (Allegra)

Desloratadine (Clarinex) was approved in 2004 in syrup form for children two years and older for seasonal allergies and for hives of unknown cause in children as young as six months. It is the only nonsedating antihistamine approved as of 2004 for children as young as six months.

Hismanal has the potential to cause serious heart arrhythmias when taken with the antibiotic erythromycin, the antifungal drugs ketoconazole and itraconazole, or the antimalarial drug quinine. Taking more than the recommended dose of Hismanal can also cause arrhythimas. Seldane (terfenadine), the original non-drowsy antihistamine, was voluntarily withdrawn from the market by its manufacturers in early 1998 because of this potential and because of the availability of an equally effective, safer alternative drug, fexofenadine.

Decongestants

Decongestants constrict blood vessels to the mucosa to counteract the effects of histamine. This decreases the amount of blood in the nasopahryngeal and sinus mucosa and reduces swelling. Nasal sprays are available that can be applied directly to the nasal lining and oral systematic preparations are available. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, insomnia, agitation, and difficulty emptying the bladder. Use of topical decongestants for longer than several days can cause loss of effectiveness and rebound congestion, in which nasal passages become more severely swollen than before treatment.

Topical corticosteroids

Topical corticosteroids reduce mucous membrane inflammation by decreasing the amount of fluid moved from the vascular spaces into the tissues. These medications reduce the recruitment of inflammatory cells as well as the synthesis of cytokines. They are available by prescription. Allergies tend to become worse as the season progresses because the immune system becomes sensitized to particular antigens and can produce a faster, stronger response. Topical corticosteroids are especially effective at reducing this seasonal sensitization because they work more slowly and last longer than most other medication types. As a result, they are best started before allergy season begins. Side effects are usually mild, but may include headaches, nosebleeds, and unpleasant taste sensations.

Bronchodilators or metered-dose inhalers (MDI)

Because allergic reactions involving the lungs cause the airways or bronchial tubes to narrow, as in asthma, bronchodilators, which cause the smooth muscle lining the airways to open or dilate, can be very effective. When inhalers are used, it is important that the patient be educated in the proper use of these medications. The inhaler should be shaken, and the patient should breathe out to expel air from the lungs. The inhaler should be placed at least two finger-breadths in front of the mouth. The medication should be aimed at the back of the throat, and the inhaler activated while breathing in quite slowly 3-4 seconds. The breath should be held for at least ten seconds, and then expelled. At least thirty to sixty seconds should pass before the inhaler is used again. Care should be taken to properly wash out the mouth and brush the teeth following use, as residual medication remains in this area with only a small amount actually reaching the lungs. Some bronchodilators used to treat acute asthma attacks include adrenaline, albuterol, Maxair, Proventil, or other "adrenoceptor stimulants," most often administered as aerosols. Successfully managing asthma and allergies can reduce the use of inhalers. This is done through good communication between the physician and patient, self-management with written action plans, avoiding allergy triggers, and through the use of preventive medications such as montelukast.

Anticholinergics

Ipratropium bromide (atrovent) and atropine sulfate are achticholinergic drugs used for the treatment of asthma. Ipratropium is used for treating asthmatics in emergency situations with a nebulizer.

Nonsteroidal drugs

MAST CELL STABILIZERS. Cromolyn sodium prevents the release of mast cell granules, thereby preventing the release of histamine and other chemicals contained in them. It acts as a preventive treatment if it is begun several weeks before the onset of the allergy season. It can also be used for year round allergy prevention. Cromolyn sodium is available as a nasal spray for allergic rhinitis and in aerosol (a suspension of particles in gas) form for asthma.

LEUKOTRIENE MODIFIERS. These medications are useful for individuals with aspirin sensitivity, sinusitis, polposis, urticaria. Examples include zafirlukast (Accolate), montelukast (Singulair), and zileuton (Zyflo). When zileuton is used, care must be taken to measure liver enzymes.

Immunotherapy

In this form of therapy, allergen is injected into the skin in increasing doses over a specific period of time. This may be helpful for patients who do not respond to medications or avoidance of allergens in the environment. This type of therapy may reduce the need for medications. A 2004 study recommended that children who have severe reactions to insect sting receive immunotherapy to protect them against future stings.

Treatment of contact dermatitis

An individual suffering from contact dermatitis should initially take steps to avoid possible sources of exposure to the offending agent. Calamine lotion applied to affected skin can reduce irritation somewhat, as can cold water compresses. Side effects of topical agents may include over-drying of the skin. In the case of acute contact dermatitis, short-term oral corticosteroid therapy may be appropriate. Moderately strong coricosteroids can also be applied as a wrap for twenty-four hours. Health care workers are especially at risk for hand eruptions due to glove use.

Treatment of anaphylaxis

The emergency condition of anaphylaxis is treated with injection of adrenaline, also known as epinephrine. People who are prone to anaphylaxis because of food or insect allergies often carry an "Epi-pen" containing adrenaline in a hypodermic needle. Other medications may be given to aid the action of the epipen. Prompt injection can prevent a more serious reaction from developing. Particular care should be taken to assess the affected individual's airway status, and he or she should be placed in a recumbent pose and vital signs determined. If a reaction resulted from insect sting or an injection, a tourniquet may need to be placed proximal to the area where the agent penetrated the skin. This should then be released at intervals of ten minutes at a time, for one to two minutes duration. If the individual does not respond to such interventions, then emergency treatment is appropriate.

Alternative treatment

Any alternative treatment for allergies begins with finding the cause and then helping the patient to avoid or eliminate the allergen, although this is not always possible. As with any alternative therapy, a physician should be consulted before initiating a new form of treatment. Education on the use of alternative agents is critical, as they are still "drugs" even though they are derived from natural sources. Various categories of alternative remedies may be helpful in allergy treatment, including:

  • antihistamines: vitamin C and the bioflavonoid hesperidin act as natural anithistamines.
  • decongestants: vitamin C, the homeopathic reme-dies Ferrum phosphoricum and Kali muriaticum (used alternately), and the dietary supplement N-acetylcysteine are believed to have decongestant effects.
  • mast cell stabilizers: the bioflavonoids quercetin and hesperidin may help stabilize mast cells.
  • immunotherapy: the herbs echinacea (Echinacea spp.) and astragalus or milk-vetch root (Astragalus membranaceus ) may possibly help to strengthen the immune system.
  • bronchodilators: the herbal remedies ephedra (Ephedra sinica, also known as ma huang in traditional Chinese medicine), khellin (Ammi visnaga ) and cramp bark (Viburnum opulus ) are believed to help open the airways.

Treatment of contact dermatitis

A variety of herbal remedies, either applied topically or taken internally, may possibly assist in the treatment of contact dermatitis. A poultice (crushed herbs applied directly to the affected area) made of jewelweed (Impatiens spp.) or chickweed (Stellaria media ) may soothe the skin. A cream or wash containing calendula (Calendula officinalis ), a natural antiseptic and anti-inflammatory agent, may help heal the rash when applied topically. Homeopathic treatment may include such remedies as Rhus toxicodendron, Apis mellifica, or Anacardium taken internally. A qualified homeopathic practitioner should be consulted to match the symptoms with the correct remedy. Care should be taken with any agent taken internally.

Prognosis

Allergies can improve over time, although they often worsen. While anaphylaxis and severe asthma are life-threatening, other allergic reactions are not. Learning to recognize and avoid allergy-provoking situations allows most people with allergies to lead normal lives.

Prevention

Avoiding allergens is the best means of limiting allergic reactions. For food allergies, there is no effective treatment except avoidance. By determining the allergens that are causing reactions, most people can learn to avoid allergic reactions from food, drugs, and contact allergens such as poison ivy or latex. The government will help now, since passing the Food Allergen Labeling and Consumer Protection Act in 2004. Beginning January 1, 2006, food manufacturers will be required to clearly state if a product contains any of the eight major food allergens that are responsible for more than 90% of allergic reactions to foods. These are milk, eggs, peanuts, tree nuts, fish, shellfish, wheat, and soy.

Airborne allergens are more difficult to avoid, although keeping dust and animal dander from collecting in the house may limit exposure. Cromolyn sodium can prevent mast cell degranulation, thereby limiting the allergic response.

Immunotherapy, also known as desensitization or allergy shots, alters the balance of antibody types in the body, thereby reducing the ability of IgE to cause allergic reactions. Immunotherapy is preceded by allergy testing to determine the precise allergens responsible. Injections involve very small but gradually increasing amounts of allergen, over several weeks or months, with periodic boosters. Full benefits may take up to several years to achieve and are not seen at all in about one in five patients. Individuals receiving all shots will be monitored closely following each shot because of the small risk of anaphylaxis, a condition that can result in difficulty breathing and a sharp drop in blood pressure.

Other drugs, such as leukotriene modifiers, are used to prevent asthma attacks and in the long-term management of allergies and asthma.

Resources

BOOKS

Hans-Uwe, Simon, editor. CRC Desk Reference for Allergy and Asthma. Boca Raton: CRC Press, 2000.

Kemp, Stephen F., and Richard Lockey, editors. Diagnostic Testing of Allergic Disease. New York: Marcel Dekker, Inc., 2000.

Lieberman, Phil, and Johh Anderson, editors. Allergic Diseases: Diagnosis and Treatment. 2nd ed. Totowa: Humana Press, Inc., 2000.

PERIODICALS

"Children With Serious Insect-sting Allergies Should Get Shots." Drug Week (September 3, 2004): 19.

"FDA Approves Clarinex Syrup for Allergies and Hives in Children." Biotech Week (September 29, 2004): 617.

"President Bush Signs Bill that Will Benefit Millions With Food Allergies." Immunotherapy Weekly (September 1, 2004): 50.

"What's New in: Asthma and Allergic Rhinitis." Pulse (September 20, 2004): 50.

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Allergies

Allergies

Definition

Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances.

Description

Allergies are among the most common of medical disorders. It is estimated that 60 million Americans, or more than one in every five people, suffer from some form of allergy, with similar proportions throughout much of the rest of the world. Allergy is the single largest reason for school absence and is a major source of lost productivity in the workplace.

Allergies are a type of immune reaction. Normally, the immune system responds to foreign microorganisms, or particles, like pollen or dust, by producing specific proteins, called antibodies, that are capable of binding to identifying molecules, or antigens, on the foreign particle. This reaction between antibody and antigen sets off a series of reactions designed to protect the body from infection. When this same series of reactions is triggered by harmless, everyday substances, it is called an allergy. The substance that causes the allergy is called an allergen.

All allergic reactions involve a special set of cells in the immune system known as mast cells. Mast cells, found in the lining of the nasal passages and eyelids, display a special type of antibody, called immunoglobulin type E (IgE), on their surface. Inside, mast cells store reactive chemicals in small packets, called granules. When the antibodies encounter allergens, they trigger release of the granules, which spill out their chemicals onto neighboring cells, including blood vessels and nerve cells. One of these chemicals, histamine, binds to the surfaces of these other cells, through special proteins called histamine receptors. Interaction of histamine with receptors on blood vessels causes neighboring cells to become leaky, leading to the fluid collection in the body's tissues, swelling, and increased redness characteristic of a runny nose and red, irritated eyes. Histamine also stimulates pain receptors, causing the itchy nose, eyes, and throat common in allergic rhinitis . In the gastrointestinal tract, these reactions lead to swelling and irritation of the intestinal lining, which causes the cramping and diarrhea typical of food allergy. Allergens that enter the circulation may cause hives , angioedema, anaphylaxis , or atopic dermatitis . Allergens on the skin usually cause a delayed hypersensitivity reaction. This type of allergic response may develop over several days following contact with the allergen, and symptoms may persist for a week or more.

Demographics

According to the National Institute of Allergy and Infectious Diseases, annually, more than 50 million Americans suffer from allergic diseases, with approximately 36 million suffering from allergic rhinitis . Upto 6 percent of the general population suffers from an allergy to latex, and children with spina bifida who have had multiple surgical procedures are at higher risk for allergic reactions to latex. Atopic dermatitis is one of the most common skin conditions and occurs commonly in infants and children. Prevalence in the United States is about 10 percent. Food allergies occur in 8 percent of children aged six years and younger. Peanut or other nut allergies affect about 3 million Americans and produce the most severe reactions. Acute allergic hives affect from 10 percent to 20 percent of Americans at some time during their lifetime, and half of those affected have symptoms for more than six months. Allergies to stinging insects occur in about 3.5 percent of Americans. According to the American Academy of Allergy, Asthma , and Immunology, if one parent has an allergic disease, a child has a 48 percent risk of developing allergies. If both parents have allergies, risk increases to 70 percent.

Causes and symptoms

Allergens enter the body through four main routes: the airways, the skin, the gastrointestinal tract, and the circulatory system.

Airborne allergens cause the sneezing, runny nose, and itchy, bloodshot eyes of allergic rhinitis (hay fever). Airborne allergens can also affect the lining of the lungs, causing asthma, or the conjunctiva of the eyes, causing allergic conjunctivitis . The most common airborne allergens are the following:

  • plant pollens
  • animal fur and dander
  • body parts and excrement from dust mites (microscopic creatures found in all houses)
  • excrement from cockroaches
  • house dust
  • mold spores
  • cigarette smoke
  • solvents
  • cleaners

Allergens in food can cause itching and swelling of the lips and throat, cramps, and diarrhea. When absorbed into the bloodstream, they may cause hives (urticaria) or more severe reactions involving recurrent, non-inflammatory swelling of the skin, mucous membranes, organs, and brain (angioedema). Some food allergens may cause anaphylaxis, a potentially life-threatening condition marked by tissue swelling, airway constriction, and drop in blood pressure. Common food allergens include the following:

  • nuts, especially peanuts, walnuts, and brazil nuts
  • fish, mollusks, and shellfish
  • eggs
  • wheat
  • milk
  • food additives and preservatives

In contact with the skin, allergens can cause reddening, itching, and blistering, called contact dermatitis . Skin reactions can also occur from allergens introduced through the airways or gastrointestinal tract. This type of reaction is known as atopic dermatitis. Dermatitis may arise from an allergic response (such as from poison ivy ) or exposure to an irritant causing nonimmune damage to skin cells (such as soap, cold, and chemical agents). Injection of allergens, from insect bites and stings or drug administration, can introduce allergens directly into the circulation, where they may cause system-wide responses (including anaphylaxis), as well as the local ones of swelling and irritation at the injection site.

Common causes of contact dermatitis include the following:

  • poison ivy, oak, and sumac
  • nickel or nickel alloys
  • latex

Insects and other arthropods whose bites or stings typically cause allergy include the following:

  • bees, wasps, and hornets
  • mosquitoes
  • fleas

The following types of drugs commonly cause allergic reactions:

  • penicillin or other antibiotics
  • flu vaccines
  • tetanus toxoid vaccine
  • gamma globulin

Children and adolescents with allergies are not equally sensitive to all allergens. Some may have severe allergic rhinitis but no food allergies, for instance, or be extremely sensitive to nuts but not to any other food. Allergies may get worse over time. For example, childhood ragweed allergy may progress to year-round dust and pollen allergy. On the other hand, a child may outgrow allergic sensitivity. Infant or childhood atopic dermatitis disappears in almost all people. More commonly, what seems to be loss of sensitivity is instead a reduced exposure to allergens or an increased tolerance for the same level of symptoms.

Symptoms depend on the specific type of allergic reaction. Allergic rhinitis is characterized by an itchy, runny nose, sneezing, and often a scratchy or irritated throat due to postnasal drip. Inflammation of the thin membrane covering the eye (allergic conjunctivitis) causes redness, irritation, and increased tearing in the eyes. Asthma causes wheezing, coughing, and shortness of breath. Symptoms of food allergies depend on the tissues most sensitive to the allergen and whether the allergen spread systemically by the circulatory system. Gastrointestinal symptoms may include swelling and tingling in the lips, tongue, palate or throat; nausea ; cramping; diarrhea; and gas. Contact dermatitis is marked by red, itchy, weepy skin blisters, and an eczema that is slow to heal. It sometimes has a characteristic pattern from the object containing the allergen, such as a glove allergy with clear demarcation on the hands, wrist, and arms where the gloves are worn, or on the earlobes by wearing earrings.

Whole-body or systemic reactions may occur from any type of allergen but are more common following ingestion or injection of an allergen. Skin reactions include the raised, red, and itchy patches called hives that characteristically blanch with pressure and resolve within 24 hours. A deeper and more extensive skin reaction, involving more extensive fluid collection and pain, is called angioedema. This response usually occurs on the extremities, fingers, toes, and parts of the head, neck, and face. Anaphylaxis is marked by airway constriction, blood pressure drop, widespread tissue swelling, heart rhythm abnormalities, and in some cases, loss of consciousness. Other symptoms may include dizziness , weakness, seizures, coughing, flushing, or cramping. The symptoms may begin within five minutes after exposure to the allergen up to one hour or more later. Commonly, this is associated with allergies to medications, foods, and insect venoms. In some individuals, anaphylaxis can occur with exercise , plasma exchange, hemodialysis, reaction to insulin, radiocontrast media used in certain types of medical tests, and on rare occasions during the administration of local anesthetics.

When to call the doctor

Parents should consult a physician when a child has repeated and prolonged symptoms. Allergic rhinitis may be mistaken for a cold or other upper respiratory infection. Usually, a fever indicates an infection. Food allergies and allergies to insect stings or medications can be especially dangerous, causing anaphylactic reactions that require emergency treatment.

Diagnosis

Allergies can often be diagnosed by a careful medical history, matching the onset of symptoms to the exposure to possible allergens. Allergy is suspected if the symptoms presented are characteristic of an allergic reaction, and this occurs repeatedly upon exposure to the suspected allergen. Allergy tests can also be conducted to determine allergens.

Skin tests

Skin tests are performed by administering a tiny dose of the suspected allergen by pricking, scratching, puncturing, or injecting the skin. The allergen is applied to the skin as an aqueous extract, usually on the back, forearms, or top of the thighs. Once in the skin, the allergen may produce a classic immune wheal and flare response (a skin lesion with a raised, white, compressible area surrounded by a red flare). The tests usually begin with prick tests or patch tests that expose the skin to small amounts of allergen to observe the response. A positive reaction occurs on the skin even if the allergen is at levels normally encountered in food or in the airways. Reactions are usually evaluated approximately 15 minutes after exposure. Intradermal skin tests involve injection of the allergen into the dermis of the skin. These tests are more sensitive and are used for allergies associated with risk of death, such as allergies to antibiotics. Skin testing may be painful for children.

Provocation tests

These tests involve the administration of allergen to elicit an immune response. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Delayed

Common childhood allergies
Type of allergy Common triggers
Food allergies Eggs, dairy products, peanuts, soy, wheat
Allergic rhinitis and asthma Pollens, molds, dust mites, animal dander, cigarette smoke
Atopic dermatitis (eczema) Food allergy (see above), irritating laundry or body soaps, scratchy fabrics, rubbing of fabric on skin, overheating
Other allergies Insect stings, medications, latex (for children who are often exposed in a medical setting), poison ivy, oak, and sumac

allergic contact dermatitis diagnosis involves similar methods by application of a skin patch with allergen to induce an allergic skin reaction. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount of the test substance administered as an opaque capsule along with a placebo control. Provocation tests are not used if anaphylaxis is a concern given the patient's medical history.

Treatment

Avoiding allergens is the first line of defense to reduce the possibility of an allergic attack. However, complete environmental control is often difficult to accomplish; hence, therapeutic interventions are usually necessary. A large number of prescription and over-the-counter drugs are available for treatment of immediate hypersensitivity reactions. Most of these products work by decreasing the ability of histamine to provoke symptoms. Other drugs counteract the effects of histamine by stimulating other systems or reducing immune responses in general.

Antihistamines

Antihistamines are drugs used to treat the symptoms of allergic rhinitis by blocking the action of histamine, a chemical released by the immune system in allergic reactions. Antihistamines are available as prescription and over-the-counter tablets, topical gels or creams, nasal sprays, and eye drops.

Commonly used antihistamines include the following:

  • diphenhydramine (Benadryl)
  • loratadine (Claritin)
  • cetirizine (Zyrtec)
  • fexofenadine (Allegra)
  • clemastine fumarate (Tavist)
  • chlorpheniramine (Chlor Trimeton)
  • brompheniramine (Dimetapp)

Decongestants

Decongestants dry up nasal passage tissues and reduce swollen nasal membranes so as to relieve congestion. Decongestants are available as nasal sprays or drops, oral tablets, or syrups. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, and agitation. Use of nasal spray decongestants for longer than four to five days can cause loss of effectiveness and rebound congestion, in which nasal passages become more severely swollen than before treatment. Saline nasal sprays, which do not contain decongestants, may be used for longer periods of time to help congestion and nasal passage irritation.

Commonly used decongestants include the following:

  • oxymetazoline (Afrin)
  • pseudoephedrine (Sudafed)
  • phenylephrine (Neo Synephrine)

Corticosteroids

Corticosteroids reduce mucous membrane inflammation and are available by prescription and taken as a series of oral tablets. Corticosteroids are also available as nasal sprays. Allergies tend to become worse as the season progresses because the immune system becomes sensitized to particular antigens and can produce a faster, stronger response. Corticosteroids are especially effective at reducing this seasonal sensitization because they work more slowly and last longer than most other medication types. Side effects may include headaches, nosebleeds, and unpleasant taste sensations. Long-term use of oral corticosteroids may cause more serious side effects, such as weight gain, cataracts, weakening bones, high blood pressure, elevated blood sugar, and easy bruising.

Mast cell stabilizers

Cromolyn sodium prevents the release of mast cell granules, thereby preventing release of histamine and the other chemicals contained in them. Cromolyn sodium is available in nasal sprays or via an inhaler. It is most frequently prescribed when allergic rhinitis is accompanied by asthma.

Immunotherapy

Immunotherapy, also known as desensitization therapy or allergy shots , alters the balance of antibody types in the body, thereby reducing the ability of IgE to cause allergic reactions. Immunotherapy is preceded by allergy testing to determine the precise allergens responsible. Injections involve very small but gradually increasing amounts of allergen, over several weeks or months, with periodic boosters. Full benefits may take up to several years to achieve and are not seen at all in about one in five patients. Individuals receiving all shots are monitored closely following each shot because of the small risk of anaphylaxis, a condition that can result in difficulty breathing and a sharp drop in blood pressure.

Treatment of contact dermatitis

An individual suffering from contact dermatitis should initially take steps to avoid possible sources of exposure to the offending agent. Calamine lotion applied to affected skin can reduce irritation somewhat, as can cold-water compresses. Topical antihistamine and corticosteroid sprays, gels, and creams are available to reduce itching. Side effects of topical agents may include overdrying of the skin. In the case of acute contact dermatitis, short-term oral corticosteroid therapy may be appropriate. Moderately strong corticosteroids can also be applied as a wrap for 24 hours. Healthcare workers are especially at risk for hand eruptions due to latex glove use.

Treatment of anaphylaxis

The emergency condition of anaphylaxis is treated with injection of adrenaline, also known as epinephrine. Children and adolescents who are prone to anaphylaxis because of food or insect allergies often carry an Epipen containing adrenaline in a hypodermic needle. Other medications may be given to aid the action of the Epipen. Prompt injection can prevent a more serious reaction from developing. Particular care should be taken to assess the affected child's airway status, and he or she should be placed in a recumbent pose and vital signs determined. Emergency treatment may be required for severe reactions.

Nutritional concerns

For children and adolescents with food allergies, all foods must be monitored to make sure that the allergen is not an ingredient or was not used during preparation. In individuals with severe food allergies to peanuts, peanut oil used to fry foods, or even the fumes produced during cooking with peanut oil have been known to cause anaphylactic shock.

Parents whose children have allergies to foods, like milk and gluten, which are common ingredients in many other foods, can purchase gluten-free foods and lactose-free foods in most grocery stores. Cookbooks dealing with allergies to these foods are also available.

Prognosis

Allergies can improve over time, although they often worsen. While anaphylaxis and severe asthma are life threatening, other allergic reactions are not. Learning to recognize and avoid allergy-provoking situations allows most children and adolescents with allergies to lead normal lives.

Prevention

Avoiding allergens is the best means of limiting allergic reactions. For food allergies, there is no effective treatment except avoidance. By determining the allergens that are causing reactions most people can learn to avoid allergic reactions from food, drugs, and contact allergens such as poison ivy or latex. Airborne allergens are more difficult to avoid. Preventive measures for airborne allergens include the following:

  • staying indoors with windows closed during the morning hours, when pollen levels are highest
  • keeping car windows up while driving
  • using a surgical face mask when outside
  • avoiding uncut fields
  • learning which trees are producing pollen in which seasons and avoiding forests at the height of pollen season
  • washing clothes and hair after being outside
  • regularly cleaning air conditioner filters in the home
  • using electrostatic filters for central air conditioning

For mold spores, the following steps will help:

  • keeping the house dry through ventilation and use of dehumidifiers
  • using a disinfectant such as diluted bleach to clean surfaces such as bathroom floors and walls
  • having air ducts cleaned and disinfected
  • cleaning and disinfecting air conditioners and coolers
  • throwing out moldy or mildewed books, shoes, pillows, or furniture

For house dust, the following steps will help:

  • vacuuming frequently and changing the bag regularly; using a bag with small pores to catch extra-fine particles
  • cleaning floors and walls with a damp mop
  • installing electrostatic filters in heating and cooling ducts and changing all filters regularly

For animal dander, the following steps will help:

  • avoiding contact if possible
  • washing hands after contact
  • vacuuming frequently
  • keeping pets out of the bedroom and off furniture, rugs, and other dander-catching surfaces
  • bathing and grooming pets frequently

Parents may find it helpful to keep an allergy journal for their child to track occurrence of allergic responses. For seasonal allergic rhinitis, they may use a calendar to note when symptoms begin and end. Documenting the level of seasonal allergens at the time can help determine when seasonal allergies tend to occur and what allergens affect the child. Local weather reports on television and on Web sites provide detailed allergen maps of pollen and mold/mildew spores. Antihistamines can then be taken as a preventive measure before symptoms begin each season. For children with allergies to foods, keeping a journal of foods eaten can help identify specific food allergens.

Parental concerns

For children who resist taking pills, many antihistamines are available as flavored chewable tablets, tablets that easily dissolve on the tongue, or flavored syrups. Because many over-the-counter allergy medicines contain multiple drugs, parents should be sure to read the prescribing and dosage information for any antihistamine their children are taking to ensure safe use.

Parents of children and adolescents with severe food and insect sting allergies that might result in sudden anaphylactic reactions should make sure that their children and any other family members and caregivers fully understand the severity of the allergic response and the need for immediate administration of epinephrine. Parents should consider having children with these severe allergies wear a medical alert bracelet.

Children with severe food allergies to whole food groups, such as milk or wheat, may require dietary management by a dietitian or nutritionist to ensure they receive the proper nutrients and a well-balanced diet. Breastfeeding mothers of highly allergic infants may need to eliminate suspected food allergens from their diets, because food proteins ingested by a mother can be transferred to the infant via breast milk. Special formulas are available for infants sensitive to breast milk, cow's milk, and soy milk.

KEY TERMS

Allergen A foreign substance that provokes an immune reaction or allergic response in some sensitive people but not in most others.

Allergic rhinitis Swelling and inflammation of the nasal membranes caused by sensitivity to airborne matter like pollen or cat hair.

Anaphylaxis Also called anaphylactic shock; a severe allergic reaction characterized by airway constriction, tissue swelling, and lowered blood pressure.

Angioedema Patches of circumscribed swelling involving the skin and its subcutaneous layers, the mucous membranes, and sometimes the organs frequently caused by an allergic reaction to drugs or food. Also called angioneurotic edema, giant urticaria, Quincke's disease, or Quincke's edema.

Antibody A special protein made by the body's immune system as a defense against foreign material (bacteria, viruses, etc.) that enters the body. It is uniquely designed to attack and neutralize the specific antigen that triggered the immune response.

Antigen A substance (usually a protein) identified as foreign by the body's immune system, triggering the release of antibodies as part of the body's immune response.

Asthma A disease in which the air passages of the lungs become inflamed and narrowed, causing wheezing, coughing, and shortness of breath.

Atopic dermatitis An intensely itchy inflammation often found on the face, in the bend of the elbow, and behind the knees of people prone to allergies. In infants and young children, this condition is called infantile eczema.

Conjunctivitis Inflammation of the conjunctiva, the mucous membrane covering the white part of the eye (sclera) and lining the inside of the eyelids also called pinkeye.

Contact dermatitis Skin inflammation as a result of contact with a foreign substance.

Granules Small packets of reactive chemicals stored within cells.

Histamine A substance released by immune system cells in response to the presence of an allergen. It stimulates widening of blood vessels and increased porousness of blood vessel walls so that fluid and protein leak out from the blood into the surrounding tissue, causing localised inflammation of the tissue.

Immune hypersensitivity reaction An allergic reaction that is mediated by mast cells and occurs within minutes of allergen contact.

Mast cells A type of immune system cell that is found in the lining of the nasal passages and eyelids. It displays a type of antibody called immunoglobulin type E (IgE) on its cell surface and participates in the allergic response by releasing histamine from intracellular granules.

Resources

BOOKS

Borrel, Marie. 60 Tips: Allergies. London: Hachette Illustrated, 2004.

Cross, Linda. How to Manage Your Child's Life-Threatening Food Allergies. Lake Forest, CA: Plumtree Press, 2004.

Dadamo, Peter J. Eat Right for Your Type Allergies. East Rutherford, NJ: Penguin Group, 2005.

Ford, Jean. Breathe Easy: A Teen's Guide to Allergies and Asthma. Broomall, PA: Mason Crest Publishers, 2005.

Taylor, R., et al. Allergy Relief and Prevention, 3rd. ed. Vancouver: Hartley and Marks, 2000.

PERIODICALS

Ansel, K. "Working with the Food-Allergic Child. Today's Dietitian. 4 (November 2002): 3639.

ORGANIZATIONS

Allergy and Asthma Network. 3554 Chain Bridge Road, Suite 200. Web site: <www.aanma.org>.

American Academy of Allergy, Asthma, and Immunology. 611 East Wells St, Milwaukee, WI 53202. Web site: <www.aaaai.org>.

Asthma and Allergy Foundation of America. 1125 15th Street NW, Suite 502, Washington, DC 20005. Web site: <www.aafa.org/>.

WEB SITES

"All About Allergies." Nemours Foundation. Available online at <www.kidshealth.org/parent/medical/allergies/allergy.html> (accessed October 26, 2004).

Jennifer E. Sisk, MA

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Allergies

Allergies

Definition

Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances.

Description

Allergies are among the most common medical disorders. It is estimated that 60 million Americans, or more than one in every five people, suffer from some form of allergy, with similar proportions throughout much of the rest of the world. Allergy is the single largest reason for school absence and is a major source of lost productivity in the workplace.

An allergy is a type of immune reaction. Normally, the immune system responds to foreign bodies, like pollen or bacteria, by producing specific proteins called antibodies that are capable of binding to identifying molecules (antigens) on the foreign body. This reaction between antibody and antigen sets off a series of reactions designed to protect the body from infection. Harmless, everyday substances trigger this same series of reactions. This is the condition known as allergy, and the offending substance is called an allergen.

Allergens enter the body through four main routes: the airways, the skin, the gastrointestinal tract, and the circulatory system.

  • Airborne allergens cause the sneezing , runny nose, and itchy, bloodshot eyes of hay fever (allergic rhinitis ). Airborne allergens can also affect the lining of the lungs, causing asthma , or the conjunctiva of the eyes, causing conjunctivitis (pink eye).
  • Allergens in food can cause itching and swelling of the lips and throat, cramps, and diarrhea . When absorbed into the bloodstream, they may cause hives or more severe reactions involving recurrent, non-inflammatory swelling of the skin, mucous membranes, organs, and brain (angioedema). Some food allergens may cause anaphylaxis, a potentially life-threatening condition marked by tissue swelling, airway constriction, and drop in blood pressure.
  • In contact with the skin, allergens can cause reddening, itching, and blistering, called contact dermatitis . Skin reactions can also occur from allergens introduced through the airways or gastrointestinal tract. This type of reaction is known as atopic dermatitis .
  • Injection of allergens, from insect bites and stings or drug administration, can introduce allergens directly into the circulation, where they may cause system-wide responses (including anaphylaxis), as well as the local responses like swelling and irritation at the injection site.

People with allergies are not equally sensitive to all allergens. Allergies may get worse over time. For example, childhood ragweed allergy may progress to year-round dust and pollen allergy. On the other hand, a person may lose allergic sensitivity. Infant or childhood atopic dermatitis disappears in almost all people. More commonly, what seems to be loss of sensitivity is instead a reduced exposure to allergens or an increased tolerance for the same level of symptoms.

Causes & symptoms

Causes

Immunologists separate allergic reactions into two main types: immediate hypersensitivity reactions, which are mainly mast cell-mediated and occur within minutes of contact with allergen, and delayed hypersensitivity reactions, mediated by T cells (a type of white blood cells) and occurring hours to days after exposure.

In the upper airways and eyes, immediate hypersensitivity reactions cause the runny nose and itchy, bloodshot eyes typical of allergic rhinitis. In the gastrointestinal tract, these reactions lead to swelling and irritation of the intestinal lining, which causes the cramping and diarrhea typical of food allergy. Allergens that enter the circulation may cause hives, angioedema, anaphylaxis, or atopic dermatitis.

Allergens on the skin usually cause delayed hypersensitivity reaction. Roving T cells contact the allergen, setting in motion a more prolonged immune response. This type of allergic response may develop over several days following contact with the allergen, and symptoms may persist for a week or more.

THE ROLE OF INHERITANCE. While allergy to specific allergens is not inherited, the likelihood of developing some type of allergy seems to be, at least for many people. If neither parent has allergies, the chances of a child developing allergy is approximately 1020%; if one parent has allergies, it is 3050%; and if both have allergies, it is 4075%.

COMMON ALLERGENS. The most common airborne allergens are the following:

  • plant pollens
  • animal fur and dander
  • body parts from house mites (microscopic creatures found in all houses)
  • house dust
  • mold spores
  • cigarette smoke
  • solvents
  • cleaners

Common food allergens include the following:

  • nuts, especially peanuts, walnuts, and Brazil nuts
  • fish, mollusks, and shellfish
  • eggs
  • wheat
  • milk
  • food additives and preservatives

Common causes of contact dermatitis include the following:

  • poison ivy, oak , and sumac
  • nickel or nickel alloys
  • latex

Insects and other arthropods whose bites or stings typically cause allergy include the following:

  • bees, wasps, and hornets
  • mosquitoes
  • fleas
  • scabies

Symptoms

Symptoms depend on the specific type of allergic reaction. Allergic rhinitis is characterized by an itchy, runny nose often with a scratchy or irritated throat due to postnasal drip. Inflammation of the thin membrane covering the eye (allergic conjunctivitis) causes redness, irritation and increased tearing in the eyes. Asthma causes wheezing , coughing, and shortness of breath. Symptoms of food allergies depend on the tissues most sensitive to the allergen and whether it is spread systemically by the circulatory system. Gastrointestinal symptoms may include swelling and tingling in the lips, tongue, palate or throat; nausea ; cramping; diarrhea; and gas . Contact dermatitis is marked by reddened, itchy, weepy skin blisters .

Whole body or systemic reactions may occur from any type of allergen, but are more common following ingestion or injection of an allergen. Skin reactions include the raised, reddened, and itchy patches called hives. A deeper and more extensive skin reaction, involving more extensive fluid collection, is called angioedema. Anaphylaxis, another reaction, is marked by difficulty breathing, blood pressure drop, widespread tissue swelling, heart rhythm abnormalities, lightheadedness, and in some cases, loss of consciousness.

Diagnosis

Allergies can often be diagnosed by a careful medical history, matching the onset of symptoms to the exposure to possible allergens. Allergy tests can be used to identify potential allergens. These tests usually begin with prick tests or patch tests, which expose the skin to small amounts of allergen to observe the response. Reaction will occur on the skin even if the allergen is normally encountered in food or in the airways. RAST testing is a blood test that measures the level of reactive antibodies in the blood. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount. Provocation tests are not used if anaphylaxis is a concern due to the patient's medical history.

Treatment

Allergic rhinitis

The following can help to relieve the symptoms of airborne allergies:

  • Stinging nettle (Urtica dioica ) has antihistamine and anti-inflammatory properties. The common dose is 300 mg four times daily.
  • Grape (Vitis vinifera ) seed extract has antihistamine and anti-inflammatory properties. The usual dose is 50 mg three times daily.
  • Ephedra (Ephedra sinicia ), also called ma huang, has anti-inflammatory activity and is proven effective in treating allergies. Taken as a tea thrice daily or 12.525 mg in capsule form. Ephedra should not be used for prolonged periods of time, as it can raise blood pressure, cause rapid heartbeat, and interfere with adrenal gland function.
  • Licorice (Glycyrrhiza glabra ) has cortisone-like activity which is anti-inflammatory, stimulates the adrenals, and relieves allergy symptoms. Can be taken as a tea or 100300 mg in capsule form. Long term use can result in sodium retention or potassium loss.
  • Chinese skullcap (Scutellaria baicalensis ) has bronchodilator activity, is an anti-inflammatory, and prevents allergic reactions. It is taken in combination with other herbs.
  • Ginkgo (Ginkgo biloba ) seeds are used in Chinese medicine for wheezing and coughing.
  • Echinacea (Echinacea species) may have antiinflammatory activity and boost the immune system.
  • Khellin (Ammi visnaga ) has bronchodilator activity.
  • Cramp (Viburnum opulus ) bark has bronchodilator activity.
  • Traditional Chinese medicine treats allergic rhinitis with various species. Patent combination medicines are: Bu Zhong Yi Qi Wan (Tonify the Middle and Augment the Qi) and Yu Ping Feng San (Jade Windscreen) are used for preventing allergies, and Bi Yan Pian (Rhinitis Infusion) is often prescribed for syptoms affecting the nose.
  • The homeopathic remedies Rhus toxicodendron, Apis mellifica, and Nux vomica have decongestant activities. They are taken internally.
  • Vitamin C has antihistamine and decongestant activities.
  • Vitamins A and E are antioxidants and help to promote normal functioning of the immune system.
  • Coenzyme Q 10 may help to promote normal functioning of the immune system.
  • Zinc may boost the immune system.
  • N-acetylcysteine may have decongestant activity.
  • Acupuncture has been shown to be as effective as antihistamine drugs in treating allergic rhinitis. It is also used to help prevent allergic reactions by strengthening the immune system.

Skin reactions

A variety of herbal remedies, either applied topically or taken internally, can assist in the treatment of contact dermatitis. A poultice made of jewelweed (Impatiens species) or chickweed (Stellaria media ) can soothe the skin. A cream or wash containing calendula (Calendula officinalis ), a natural antiseptic and anti-inflammatory agent, can help heal the rash. Chinese herbal remedies have been effective in treating atopic dermatitis. The following are homeopathic remedies to be taken internally:

  • Apis (Apis mellifica ) for hives that feel better with cold application and bee stings
  • Poison ivy (Rhus toxicodendron ) for hives that feel better with hot applications and for poison ivy, oak, or sumac rashes
  • Stinging nettle (Urtica urens ) for hives
  • Marsh tea (Ledum ) for itching insect bites
  • Croton (Croton tiglium ) oil for poison ivy, oak, or sumac rashes

Food allergies

Food allergy may be managed by oral desensitization. Children with allergy to milk, eggs, fish, or apples who followed an oral desensitization procedure developed resistance to the allergenic food. Oral desensitization exposes the patient to allergens in controlled, but increasing, doses. Control subjects, who had avoided the allergenic food during the study, were still sensitive.

Allopathic treatment

A large number of prescription and over-the-counter drugs are available for treatment of immediate hypersensitivity reactions. Most of these drugs work by decreasing the ability of histamine to provoke symptoms. Other drugs counteract the effects of histamine by stimulating other systems or reducing immune responses in general.

ANTIHISTAMINES. Antihistamines block the histamine receptors on nasal tissue, decreasing the effect of histamine released by mast cells. They may be used after symptoms appear, though they seem to prove more effective when used preventively. A wide variety of antihistamines are available.

DECONGESTANTS. Decongestants constrict blood vessels to counteract the effects of histamine. Nasal sprays and oral systemic preparations are available. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, and agitation. Use of nasal sprays for longer than several days can cause loss of effectiveness and rebound congestion, in which nasal passages become more severely swollen than before treatment.

TOPICAL CORTICOSTEROIDS. Topical corticosteroids reduce mucous membrane and skin inflammation and are available by prescription. Allergies tend to become worse as the season progresses and topical corticosteroids are especially effective at reducing this seasonal sensitization. As a result, they are best started before allergy season begins. A 2001 study revealed that steroid nasal sprays work better for seasonal allergies on an as-needed basis than do antihistamines. Side effects are usually mild, but may include headaches, nosebleeds , and unpleasant taste sensations.

MAST CELL STABILIZERS. Cromolyn sodium prevents the release of mast cell granules, thereby preventing the release of histamine and other chemicals contained in them. Cromolyn sodium is available as a nasal spray and aerosol (a suspension of particles in gas).

BRONCHODILATORS. Because allergic reactions involving the lungs cause the airways or bronchial tubes to narrow, bronchodilators, which cause the smooth muscle lining the airways to open, can be very effective. Bronchodilators include adrenaline, albuterol, and theophylline. Other drugs, including steroids, are used to prevent and control asthma attacks.

Immunotherapy

Immunotherapy, also known as desensitization or allergy shots, alters the balance of antibody types in the body. Injections involve gradually increasing amounts of allergen, over several weeks or months, with periodic boosters. Full benefits may take up to several years to achieve and are not seen at all in about one in five patients. Individuals receiving all shots will be monitored closely following each shot because of the small risk of anaphylaxis, a condition that can result in difficulty breathing and a sharp drop in blood pressure.

Possible future treatments

In late 2001, a reports stated that a monoclonal antibody called omalizumab might be effective in treating seasonal allergies and preventing related asthma. By blocking immunoglobulin E (IgE), an antibody that is found in excessive amounts in those with hay fever , the drug treats hay fever and helps prevent related asthma. Trials on the drug continue, and other immune-based medicines will likely accompany its ultimate release.

Treatment of contact dermatitis

Calamine lotion applied to affected skin can reduce irritation somewhat. Topical corticosteroid creams are more effective, though overuse may lead to dry and scaly skin.

Treatment of anaphylaxis

The emergency condition of anaphylaxis is treated with injection of adrenaline, also known as epinephrine. People who are prone to anaphylaxis because of food or insect allergies often carry an "Epi-pen" containing adrenaline in a hypodermic needle. Prompt injection can prevent a more serious reaction from developing.

Expected results

Allergies can improve over time, although they often worsen. While anaphylaxis and severe asthma are life-threatening, other allergic reactions are not. Learning to recognize and avoid allergy-provoking situations allows most people with allergies to lead normal lives.

Prevention

By determining which allergens are causing the reactions, most people can learn to avoid allergic reactions from food, drugs, and contact allergens. Airborne allergens are more difficult to avoid, although keeping dust and animal dander from collecting in the house may limit exposure. Vitamin C may prevent allergy symptoms. Cromolyn sodium can be used for allergy prevention.

Resources

BOOKS

Lawlor G.J., Jr, T.J. Fischer, and D.C. Adelman. Manual of Allergy and Immunology. Boston: Little, Brown and Co., 1995.

Weil, A. Natural Health, Natural Medicine: A Comprehensive Manual for Wellness and Self-Care. Boston: Houghton Mifflin, 1995.

Ying, Zhou Zhong and Jin Hui De. "Common Diseases of Otorhinolaryngology and Stomatology." In Clinical Manual of Chinese Herbal Medicine and Acupuncture. New York: Churchill Livingston, 1997.

PERIODICALS

Harder, Patty A. "Homeopathic First-Aid for Allergic Reactions." Better Nutrition. 60 (June 1998): 42.

Patriarca, G., D. Schiavino, E. Nucera, G. Schinco, A. Milani, and G.B. Gasbarrini. "Food Allergy in Children: Results of a Standardized Protocol for Oral Desensitization." Hepato-Gastroenterology. 45 (1998): 52-58.

Plaut, Marshall. "Immune-Based, Tageted Therapy for Allergic Diseases." JAMA, The Journal of the American Medical Association. (December 19, 2001): 3005.

Siegel-Maier, Karyn. "Nettlesome Allergies! Natural Alternatives to Treat Seasonal Sneezing." Mother Earth News. (September 1998): 24+.

"Steroid Nasal Spray Better for Season Allergies than Antihistamines." Immunotherapy Weekly (December 12, 2001): 12.

Belinda Rowland

Teresa Norris

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Allergies

ALLERGIES

ALLERGIES. Food allergy has been recognized since the time of Hippocrates. People with adverse reactions to food can be difficult to evaluate because overlap exists between true food allergy and toxic and other reactions to chemicals or other food ingredients. The incidence of food allergy is increasing in the industrialized world, raising questions about the interactive effects between environmental and genetic factors. There is a considerable burden on society in terms of cost of treatment, death from anaphylactic reactions, and the anxiety produced by real or perceived food allergy. Avoidance of the food is the current treatment, but new strategies are being developed.

Definitions

Adverse reactions to the ingestion of food that can be reproduced is termed intolerance or hypersensitivity. Since this does not imply an underlying cause, it may encompass immune or nonimmune mechanisms. For example, chemicals such as caffeine may cause reproducible symptoms, but this is not mediated by the immune system. True food allergy or food hypersensitivity is defined as a reproducible adverse reaction to food caused by the immune system creating antibodies or cellular inflammation.

Type I IgE-mediated food allergy. The classic example is immediate anaphylactic reaction to food. In susceptible individuals after exposure to the food, the immune system creates specific IgE antibodies to that food. IgE is produced by the immune system's B-lymphocytes, and is bound to receptors on the surface of mast cells. Mast cells reside in tissues at body surfaces such as the skin, eyes, nose, throat, lung, and gastrointestinal tract. Mast cells are made up of granules containing chemicals including histamine. When the food protein contacts and binds to adjacent specific IgE molecules at the mast cell surface, a cascade of events occurs leading to degranulation of mast cells and release of chemicals that cause the allergic reaction. This may include skin hives, airway swelling, wheezing, abdominal pain, vomiting and/or diarrhea. This may progress to anaphylaxis, shock, and even death. This reactivity to food can be demonstrated by skin-prick tests, which have been used to diagnose allergy since the 1870s. Food protein is placed on the skin, the skin is scratched or pricked, and a hive will develop in the presence of skin mast cells with IgE directed against the food. In the 1920s Prausnitz and Kustner showed that a substance circulating in the blood of the allergic individual was responsible for a positive skin test, because blood serum could be transferred to the skin of a nonallergic individual resulting in a positive skin test. IgE is that substance, and food-specific IgE can be measured directly in the blood, by means of the IgE RAST (radioallergosorbent) test. Diagnosis of this immediate type of food allergy rests on the history of rapid onset of symptoms, demonstration of positive skin-prick test or specific IgE RAST. Challenging an individual with the food is the ultimate way to prove a food allergy.

Non-IgE-mediated food allergy. Other immune mechanisms can be responsible for allergic reactions to foods. The classic example is celiac disease (celiac sprue or gluten-induced enteropathy). This is an immune system reaction to wheat (gluten). Patients do not have IgE antibody directed against wheat, but exposure to gluten over a period of time causes inflammation of the intestine and a characteristic atrophy or flattening of the normal intestinal villous folds. The diagnosis rests on the characteristic biopsy of the small intestine coupled with another type of antibody (IgA) against wheat protein. Any food may also cause similar intestinal inflammation, leading to varying symptoms and signs depending on the area of the intestine affected. Unlike IgE-mediated allergy or celiac disease, there are no readily available confirmatory tests for these other food allergies.

Prevalence

Food allergy is perceived as being common; however, large studies support the idea that true food allergy is less common than people think. A study of 480 infants from birth to age three revealed 28 percent were suspected by their parents as having food allergy; however, this was confirmed in only 8 percent of this group. The prevalence then decreases with age. Twenty percent of adults suspect food allergy, though allergy is confirmed in only 1 to 2 percent of adults. Although food allergies in adults tend to persist with age, many infants and children out-grow them with time.

Recently, interest has grown over the apparent increase in the prevalence and severity of food allergy. This has paralleled an increase in other atopic disorders such as asthma in industrialized nations compared with children of similar genetic background in developing countries (atopic refers to a tendency to develop allergic conditions such as hay fever, asthma, or food allergies). The "hygiene hypothesis" contends that through evolution, the human immune system has developed with a specific microbial environment, and reduced exposure to microbes in the developed world may lead to increased allergic response. Further study is needed.

Type I Immediate (IgE-Mediated) Hypersensitivity Reactions to Food

Immediate hypersensitivity reactions to foods are most common in young children, with 50 percent of these reactions occurring in the first year of life. The majority is from cow's milk and soy protein from infant formulas. Other foods begin to predominate in older children, including eggs, fish, peanuts, and wheat, and along with milk and soy account for over 90 percent of food allergy in children. Peanut, tree nut, and shellfish allergy predominate in adults. Exposures may occur inadvertently due to improper labeling, changes in product composition with time, and contamination of foods during processing. Symptoms from multiple organ systems may occur, beginning within minutes. Unfortunately, fatal anaphylactic reactions (shock) to food occur despite strict dietary avoidance and treatment of reactions. Families, caregivers, and individuals with a history of anaphylaxis to food require education in diet and in the use of self-administered epinephrine. Individuals should be observed in a hospital setting after a significant reaction. Exercise-induced anaphylaxis to food occurs when the combination of ingesting the food followed by exercise leads to anaphylaxis. Oral allergy syndrome describes symptoms of itching of the mouth and throat often attributable to eating fruits, and typically does not progress. Chronic hives or urticaria can be caused by foods, but it is a common misconception that these conditions are usually food-related; only in 1 to 2 percent of cases is urticaria or chronic hives a reaction to food. Atopic dermatitis (AD) or eczema is a chronic skin condition found in atopic individuals. Patients with AD have a 30 to 40 percent prevalence of food allergy.

Investigation and treatment of type I immediate reactions to food. The rapid onset of symptoms after ingestion correlates highly with positive skin-prick or IgE RAST tests to the offending food, making confirmation of immediate hypersensitivity straightforward. Consultation with an allergist and dietitian is recommended. Groups such as the Food Allergy and Anaphylaxis Network can provide support and educational materials.

Non-IgE-Mediated Food Allergy

The spectrum of non-IgE food allergy is quite varied, and the symptoms often parallel the area of inflammation in the gastrointestinal tract (see sidebar). Avoidance of the food will resolve symptoms and intestinal inflammation; rechallenge with the food will reproduce the injury. However, unlike IgE food allergy, symptoms may take days or weeks to resolve or reappear with elimination or exposure respectively, making evaluation even more difficult.

Celiac disease or gluten-induced enteropathy (see sidebar) is a chronic intestinal condition caused by non-IgE mediated allergy to gluten, a protein in wheat and other grains. Chronic exposure to gluten causes inflammation and atrophy of small intestinal folds, leading to symptoms of malabsorption of food. Typically, patients have diarrhea, weight loss, and abdominal bloating. There is a genetic predisposition to celiac disease, but onset may occur at any age, suggesting an environmental factor such as infection may be needed in some individuals to trigger the inflammatory process. The disease has a higher prevalence (up to 1 in 400500) in individuals of eastern European descent. Celiac disease is associated with a skin condition (dermatitis herpetiformis), thyroid disease, diabetes, and Down syndrome.

Allergic or eosinophilic colitis in infants is a common manifestation of non-IgE food protein allergy. It is characterized by diarrhea with blood and mucus. It is caused by milk or soy formula and may occur in breast-fed infants from dietary antigens transmitted through breast milk. Colon biopsy shows allergic inflammation.

Food protein-induced enterocolitis is a severe reaction to food, often delayed four to six hours, without evidence of IgE. Patients present with lethargy, vomiting, and diarrhea. Recovery is within six to eight hours after fluid resuscitation. A careful history usually reveals the offending food, although this may not be appreciated unless multiple episodes occur.

Chronic enteropathy from food allergy can also lead to inflammation with villous atrophy similar to celiac disease. Most patients have diarrhea, in addition to weight loss, anemia, and low albumin from protein loss from the intestine.

Allergic gastritis is inflammation of the stomach with pain and vomiting. As with other non-IgE food allergy, biopsies of the stomach demonstrate allergic (eosinophilic) inflammation.

Allergic esophagitis is characterized by intense eosinophilia of the esophagus on biopsy. Patients complain of pain and problems with swallowing, even to the point of having food impactions in the esophagus. Treatment with hypoallergenic formula has been shown to improve esophagitis in infants; however, older children and adults may require corticosteroid medication.

Infantile colic and excessive irritability can be symptoms related to allergy in a subgroup of infants. By definition, colic is a condition with increased crying behavior in infants, for which no cause can be found. However, since allergy can potentially lead to inflammation and pain, formula allergy is often considered.

Attempts have been made to associate a variety of other problems with food allergy including joint disease, migraine, and behavioral and developmental disorders such as autism. Causal relationship between food allergy and these disorders remains unproven.

Investigation and treatment of non-IgE-mediated food allergy. The diagnosis rests on the resolution of symptoms and/or biopsy findings on an elimination diet, with a return of symptoms on rechallenge. Unlike the rapid response characteristic of IgE-mediated disease, a prolonged challenge may identify delayed reactions with predominantly gastrointestinal symptoms up to six days after exposure. Elemental diets can be used to eliminate dietary protein antigens completely, then systematic rechallenge of the patient with suspected offending foods. As with IgE food allergies, avoidance of the specific food remains the mainstay of therapy.

New Frontiers

There are a number of exciting areas of research into the prevention and treatment of food allergies. Recent reports suggest that the allergic response can be altered by promoting beneficial gut flora ("probiotic therapy"). It has also been discovered that only a few sites (epitopes) on food protein molecules interact with the immune system to create an allergic reaction. Genetic engineering of foods makes it possible to alter these epitopes, creating crops that are "nonallergic." More study is needed to ensure that altering food proteins does not lead to other health concerns or different types of allergy. Other studies are under way to assess the effectiveness of promising new drug therapies for patients with food allergy.

See also Aversion to Food ; Baby Food ; Health and Disease ; Immune System Regulation and Nutrients ; Milk, Human ; Proteins and Amino Acids .

BIBLIOGRAPHY

Justinich, Christopher J. "Food Allergy and Eosinophilic Gastroenteropathy." In Pediatric Gastroenterology, vol. 2, edited by Jeffrey S. Hyams and Robert Wyllie, pp. 334347. Philadelphia: W. B. Saunders, 1999.

Metcalfe, Dean D., H. A. Sampson, and R. A. Simon, eds. Food Allergy: Adverse Reactions to Food and Food Additives. 2d ed, Cambridge, Mass.: Blackwell Science, 1997.

Sampson, H. A. "Food Allergy. Part 2: Diagnosis and Management." Journal of Allergy and Clinical Immunology 103 (1999): 981989.

Sampson, H. A. "Food Allergy. Part 1: Immunopathogenesis and Clinical Disorders." Journal of Allergy and Clinical Immunology 103 (1999): 717728.

Sampson, H. A., and J. A. Anderson. "Classification of Gastrointestinal Disease of Infants and Children due to Adverse Immunologic Reactions to Foods." Journal of Pediatric Gastroenterology and Nutrition 30 (suppl) (2000): 194.

Christopher J. Justinich


Manifestations of IgE Allergy to Food

Cardiovascular (shock)
Respiratory (wheeze, cough)
Gastrointestinal (acute vomiting, pain, diarrhea)
Skin (hives, atopic dermatitis)
Eye (itching, swelling)
Oral (itching, swelling)

Manifestations of Non-IgE Allergy to Food

Growth delay
Protein-losing enteropathy, edema
Iron-deficiency anemia
Chronic diarrhea
Eosinophilic colitis
Chronic vomiting/feeding intolerance
Food protein-induced enterocolitis syndrome
Atopic dermatitis
Infantile colic

Manifestations of Celiac Disease (Gluten-Induced Enteropathy)

Growth delay
Chronic diarrhea
Abdominal distension
Abdominal pain
Dermatitis herpetiformis
Associations: Diabetes, thyroid disease, Down syndrome

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Allergy

Allergy

An allergy is an extreme or overly sensitive response of the immune system to harmless substances in the environment. The immune system launches a complex series of actions against an irritating substance, referred to as an allergen. This immune response may be accompanied by a number of stressful symptoms, ranging from mild to severe to life-threatening. In rare cases, an allergic reaction leads to anaphylactic shocka condition characterized by a sudden drop in blood pressure, difficulty in breathing, skin irritation, collapse, and possible death.

The immune system may produce several chemical agents that cause allergic reactions. One example are the histamines released after exposure to an allergen. (Histamines are compounds that cause capillaries to dilate; smooth muscles to contract, thereby constricting airways; and gastric acids to be secreted.) The use of antihistamines helps to relieve some of the symptoms of allergy by blocking out histamine receptor sites in cells.

Types of allergy

The most common type of allergy is allergic rhinitis (inflammation of the mucous membrane of the nose) caused by inhaling allergens carried in the air. Seasonal environmental allergic rhinitis, or hay fever as it is popularly called, is brought on by wind-borne pollens, the dustlike masses of microscopic spores in seedbearing plants. Every spring, summer, and fall, pollens from grasses, trees, and weeds produce allergic reactionslike sneezing, runny nose, swollen nasal tissues, headaches, blocked sinuses, and watery, irritated eyesin allergy-prone people. Perennial allergic rhinitis is the year-round occurrence of symptoms caused by inhaling allergens such as animal dander, molds, and dust from dust mites. Of the 46 million allergy sufferers in the United States, about 25 million have rhinitis.

Words to Know

Allergen: An otherwise harmless substance that causes a fixed allergic response in certain people.

Anaphylactic shock: A violent, sometimes fatal, response to an allergen after initial contact.

Decongestant: Drug used for a short term to reduce mucous membrane congestion.

Histamine: Chemical produced by the immune system that triggers allergic reactions.

IgE: The chief antibody responsible for producing the compounds that cause allergic reactions.

Lymphocyte: A white blood cell that stimulates antibody formation.

Mast cell: A large cell in connective tissue containing substances involved in allergic reactions.

Receptor sites: Places on cells where substances bind to produce certain reactions.

Rhinitis: Nasal congestion, inflammation, and sneezing caused by seasonal pollens or other allergens.

Steroids: Drugs that stimulate the adrenal glands (which in turn secrete hormones, or chemical messengers that regulate various bodily functions) and are highly effective in treating asthma and allergies but also have many side effects.

Weal: A welt; the reddened, itchy swelling caused by a skin patch test.

Other types of allergies can be traced to certain foods, drugs, insect bites, skin contact with chemical substances, and odors. In the United States there are about 12 million people who are allergic to a variety of chemicals. In some cases an allergic reaction to an insect sting or a drug can cause sudden death. Serious asthma attacks are associated with seasonal rhinitis and other allergies. About 9 million people in the United States suffer from asthma.

Role of immune system

An individual's immune system plays a part in determining both the occurrence and the severity of allergic reactions. Some people are allergic to a wide range of allergens while others are allergic to only a few or to none. The immune system is the body's defense against substances it recognizes as foreign invaders. Lymphocytes, a type of white blood cell, fight viruses, bacteria, and other antigens (foreign substances such as toxins or enzymes) by producing antibodies. When an allergen first enters the body, the lymphocytes produce an antibody called immunoglobulin E

(IgE). The IgE antibodies attach to mast cells, large cells in connective tissue that contain histamines and other chemicals. The second time any given allergen enters the body, it becomes attached to the newly formed, Y-shaped IgE antibodies. These antibodies, in turn, stimulate the mast cells to release their histamines and other anti-allergen chemicals.

Studies show that allergy sufferers produce an excessive amount of IgE, indicating a hereditary factor in their allergic responses. How individuals adjust over time to allergens in their environment is also a factor in determining whether they will develop an allergic disorder.

Anaphylaxis

Anaphylaxis is a sudden, severe, sometimes fatal allergic reaction to a foreign substance or antigen. In humans, anaphylaxis is a rare event in which an initial exposure to a certain substancesuch as penicillin, an insect sting, or certain foodscreates extreme sensitivity to it. The body reacts to the allergen by producing specific immunoglobulin E (IgE) antibodies that attach to the surface of mast cells containing histamine. On subsequent exposure to the allergen, the antigen binds with the specific IgE antibodies, triggering the immediate release of histamine and other irritating chemicals by the mast cells. The release of these chemicals cause hives, itching, nasal congestion, a sudden drop in blood pressure, shock, or loss of consciousness. Swelling of the upper respiratory tract may result in severe difficulty breathing, which can lead to death.

Anaphylaxis must be treated immediately with an injection of adrenaline, followed by other medications. To prevent anaphylaxis, individuals with known sensitivities to certain substances are instructed to avoid exposure to them. Anaphylaxis kits are sometimes prescribed by doctors for patients who are hypersensitive to one or more antigens (a bee's sting, for instance). In the event of an emergency, the patients can inject themselves with adrenaline provided in the kit before getting to a doctor or hospital.

Diagnosis and treatment

Diagnosis of an allergic disorder is based primarily on the patient's medical history. Skin patch tests are sometimes used to determine exactly which allergens aggravate the patient's condition. A tiny amount of a suspected allergen is injected under the skin; any actual allergen will raise a weal at the site of the injection. The weal is a circular area of swelling that itches and is reddened. The size of the weal produced by a suspected allergen is compared to a "control" weal produced by the injection of histamine itself. The tests at times produce false positives, so they cannot be relied on exclusively.

The simplest form of treatment is avoidance of the allergic substance. When that is not possible, desensitization to the allergen is sometimes attempted by exposing the patient to gradually increasing quantities of the allergen at regular intervals.

Antihistamines, which are now prescribed and sold over the counter as an allergy remedy, were discovered in the 1940s. Antihistamines act by occupying the receptor sites in cells that react to histamine; histamine is therefore blocked from entering the sites. The allergens are still there, but the body's protective actions are suspended for the time the antihistamines are active. Antihistamines also constrict the smaller blood vessels and capillaries, thereby preventing the accumulation of excess nasal fluids.

Steroid drugs inhaled through the nose are sometimes prescribed to allergy sufferers to relieve local inflammation. Decongestants can also bring relief but should only be taken for a short time, since their continued use can make the allergy-sufferer's reaction more intense.

[See also Antibody and antigen; Immune system ]

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allergy

allergy Every spring and summer, many people suffer from hay fever, a very common form of allergy. The symptoms include itchy eyes, sneezing, and congested nostrils. Most of these symptoms can be controlled by antihistamine or steroid nasal spray. Unfortunately, in some forms of allergy, violent reactions may take place leading to serious or even fatal consequences — anaphylactic shock — as seen in allergies to seafood, nuts, or certain drugs such as penicillin.

In the realm of immunology, substances that cause immune responses or allergic reactions are known as antigens. Specific antigens that provoke an allergic reaction are called allergens. Typical allergens include pollens, house-dust mites, animal dander, bacteria, foods, drugs, and chemicals. At present, we do not know why, in similar amounts and circumstances, these substances are harmless to most people but can cause health hazards in others. Avoidance of known allergens is the best protection against such reactions.

In the immune system several mechanisms have been evolved to protect the body against antigens. Prominent among these are the lymphocytes, white blood cells that are specialized to react to specific antigens. There are two kinds of lymphocytes — B cells and T cells. B cells produce antibodies, which are proteins that bind to and destroy or neutralize antigens. T cells do not produce antibodies; instead, they produce cytokines — soluble molecules mediating interaction between cells. T cells also bind directly to an antigen and initiate an attack on it by ‘presenting’ parts of it to B cells, to stimulate antibody production.

Allergic reactions

Depending on whether the antigen triggers a response by B cells or T cells, allergic (hypersensitivity) reactions can have immediate or delayed effects. They are classified as Type I, II, III, and IV. Type I, II, and III allergic reactions are the products of B cell stimulation, and, as a result of antibody–antigen responses, these reactions take immediate effect. Different types of reaction may occur together — for example, in asthma, bronchial reactions to allergens show both an immediate and a late-phase response.

Type I reactions;

which include hay fever and insect venom allergy, involve the class of antibodies known as immunoglobulin E (IgE). IgE molecules are bound to mast cells, which are found in connective tissue. When enough antigen has bound with the IgE antibodies, the mast cells release granules of histamine and heparin and produce other substances that cause inflammation. These potent chemicals dilate blood vessels and constrict bronchial air passages. Histamine is responsible for the visible symptoms of an allergic attack, such as running nose, wheezing, and tissue swelling. Antihistamines or steroid nasal spray are often used to give temporary relief. An alternative treatment is desensitization, in which increasing amounts of the antigen are injected over a period of time until the sufferer no longer experiences an allergic response.

In severe allergic reactions, ‘complement’ fragments (anaphylatoxins) — proteins circulating in the blood — stimulate a more massive release of substances from mast cells which dilate blood vessels and constrict bronchioles. This sequence of events results in the collapse of the circulatory system, together with respiratory symptoms, leading to a potentially fatal reaction — anaphylactic shock.

Drug allergy is a hypersensitivity reaction to therapeutic agents. It occurs occasionally on second exposure to a drug against which an individual has already produced antibodies. It remains to be established why some drugs rarely cause allergic reactions (e.g. tetracyclines, digitalis), while others frequently provoke them (e.g. penicillin, phenytoin).

The mechanisms of immune activation in drug allergy are similar to antibody responses to foreign molecules, especially proteins, that enter the body. Although drug molecules are too small to be antigenic by themselves, they can conjugate to body proteins and elicit an immune response. Symptoms vary with the drug and the sensitivity of the affected person, but include, as separate reactions, hives (urticaria), serum sickness, and, sometimes, anaphylaxis. Several drugs can successfully counteract these allergic symptoms (antihistamines, cromolyn, and corticosteroids) — but at present, the best way to combat drug allergy is to identify the offending drug and to observe a lifelong avoidance of that particular compound and its derivatives.

Type II reactions

involve different immunoglobulins, known as IgG or IgM, which are antibodies against antigens on the surface of certain ‘target’ cells or in their immediate environment. These antigens may be natural components of healthy cells, or they may be extrinsic components induced by drugs or infectious microbes. The resulting antigen–antibody complex activates the complement system: a series of potent enzymes that destroy the target cell. An example of Type II reactions is autoimmune haemolytic anaemia. In patients with this condition, antibodies destroy their own red blood cells, leading to anaemia.

Type III reactions

result when the antigen– antibody complexes (immune complexes) become deposited on the walls of the small blood vessels. Normally, phagocytes remove immune complexes effectively. However, if this mechanism is overloaded, the immune complexes persist and are eventually deposited in a range of tissues and organs. These complexes then trigger the complement system, resulting in damage to blood vessels and inflammation; an example is glomerulonephritis, when the ‘filtering’ components of the kidneys are affected.

Type IV

allergic reactions are the only ones that involve delayed hypersensitivity. These reactions are caused by the actions of T cells. Here the antigens are trapped inside macrophages and cannot be cleared. T cells are then activated to produce cytokines, which mediate a range of inflammatory responses. In contrast to the rapid responses mediated by B-cell antibodies, T cells take longer to accumulate at the site where the antigen is present. Thus the allergic responses are delayed and appear 12 to 24 hours or more after exposure to an appropriate antigen. Contact dermatitis is one example, in which the skin responds to allergens such as nickel and rubber accelerators. These substances penetrate the skin and become linked to a carrier protein, capable of producing allergic reactions.

Hypersensitivity involving T-cell-mediated immunity occurs also in some chronic diseases due to infectious agents such as the mycobacteria that cause leprosy and tuberculosis, and parasitic worms such as schistosomiasis.

Organ transplantation (of kidney, heart, or lungs, respectively) is increasingly used to save patients with renal failure, cardiac failure, or cystic fibrosis. Unfortunately, T cells of the recipients can recognize and respond to foreign antigens of the grafts, leading to their eventual destruction. Immunosuppressive drugs such as steroids and cyclosporin are successful in preventing rejection. However, these drugs do not work specifically against the particular unwanted functions of macrophages or T-cells, and may reduce the patients' resistance to infections.

Tai-Ping Fan


See also autoimmune disease; phagocytes; thymus.

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Allergy

ALLERGY

Treatment of allergies became a part of psychosomatics, and subsequently psychoanalysis, following the work of the Chicago School, especially Franz Alexander and Thomas M. French in 1941. Alexander and French focused primarily on asthma rather than cutaneous allergic reactions, but later authors approached these initial studies quite differently. Distancing themselves from the idea of hysterical conversion, they established a link between psychic conflict and analogous somatic conflict. With respect to allergy, they looked for the conflicting elements they considered characteristic. For asthma, these conflicts were primarily conflicts between infants' dependence on their mothers and instinctual demands that threatened this dependence. The crisis itself was associated with an inhibition of emotional expression, especially tears.

Because these factors were not specific, other authors returned to classical methods of analysis. Phyllis Greenacre (1945) insisted that oral sadism can be masked by streams of crocodile tears; here emotional expression assumes renewed importance in an interpretive framework. Jacob Arlow (1955) considered an allergic attack to be a manifestation of transference essentially associated with sadistic fantasies of incorporation. Melitta Sperling (1963) also demonstrated the links between allergies and pregenital factors. Philip C. Wilson (1968) hypothesized that transferential acting may be involved. In the end, the dimension of conversion returned to the foreground. Michel de M'Uzan (1968) insisted on the need to clarify the formation of somatic symptoms, and he turned to the notion of psychosomatic structure.

Pierre Marty reinvigorated the concept of allergies through his description of the allergic character (1976), which followed his account of the allergic object relation fifteen years earlier. He gave the allergic character the following traits: absence or avoidance of aggressiveness, a capacity for identification, absence or avoidance of conflict, considerable merging with the other, and projection as a mode of identification. To describe these traits in turn, absence or avoidance of aggressiveness gives subjects a socially agreeable cast, but is based on a weak capacity for negation, which in turn indicates a weak superego. The capacity for identification was already included in the allergic object relation. Merging with the other (absence of anxiety in the face of the foreign) is also characteristic of certain forms of primary epilepsy and allergic epilepsy, described by Marie-Thérèse Neyraut-Sutterman. Projection, described in 1957, becomes a mode of identification. As a consequence, subjects are unable to project bad objects or to distinguish good from bad.

Only when the allergic child is able, through stranger anxiety, to be afraid do allergic mechanisms begin to diminish. The features above can be found together in a character neurosis (which Pierre Marty referred to as a common allergy bundle), or they can appear as simple, relatively invasive traits that form a more or less split-off component of the personality, manifested only during regression (Pierre Marty referred to these as lateral lines) or deep splitting (parallel lines).

An allergic crisis can be triggered by the overriding of identificatory possibilities, as when the child is presented with two equally invested objects where the identifications have been kept separate. For Pierre Marty, a somatic manifestation is seen as a way station within a regressive movement and not, as in the psychogenetic approach, as the somatic expression of a traumatic situation. For Michel Fain, the unconscious of the typical allergic is the seat of the mother's desire to have the child regress to a primary narcissistic stage of feelings of unity with her, a desire that keeps an entire portion of the ego of the allergic patient in an embryonic state.

For Marty, these properties and variations result in distinct therapeutic indications. In typical cases, the allergic individual is very adaptable, also in the allergic's relation to the analyst and to analysis. The down side of this is that there is a risk of an outbreak of somatic manifestations at the end of treatment. He therefore recommends psychotherapy as a prophylactic, which can help the patient to recognize unconscious factors and become aware of the danger of certain object relations. Marty believes that medical treatment is indicated for somatic disorders, and that analysis and psychotherapy should not be recommended for allergic manifestations.

This conception of an allergic quasi-structure has led to more recent work by Léon Kreisler (1982), Michel Fain (1969), and Gérard Szwec (1993), who have addressed these problems in children.

Robert AssÉo

See also: Allergic object relationship; Asthma.

Bibliography

Alexander, Franz, and French, Thomas M. (1941). Psychogenic factors in bronchial asthma. Washington, DC: National Research Council.

Arlow, Jacob. (1955). Notes on oral symbolism. Psychoanalytic Quarterly, 24, 63-74.

Fain, Michel. (1969). Réflexions sur la structure allergique. Revue française de psychanalyse, 33 (2).

Greenacre, Phyllis. (1945). Pathological weeping. Psychoanalytic Quarterly, 14 62-75.

Kreisler, Léon. (1982). L'économie psychosomatique de l'enfant asthmatique:à propos d'un cas d'asthme grave chez un préadolescent Psychothérapies, 2 (1), 15-24.

Marty, Pierre. (1976). Les mouvements individuels de vie et de mort. Vol. 1: Essai d'économie psychosomatique. Paris: Payot.

M'Uzan, Michel de. (1968). Comment on "Psychosomatic Asthma and Acting Out," by Ph. Wilson. International Journal of Psycho-Analysis, 49 (2-3), 333-335.

Sperling, Melitta. (1963). Fetishism in children. Psychoanalytic Quarterly, 32, 374-392.

Szwec, Gérard. (1993). La psychosomatique de l'enfant asthmatique. Paris: Presses Universitaires de France.

Wilson, C. Philip. (1968). Psychosomatic asthma and acting out: A case of bronchial asthma that developed de novo in the terminal phase. International Journal of Psycho-Analysis, 49 (2-3), 330-333.

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Allergies

Allergies

An allergy is an excessive or hypersensitive response of the immune system to harmless substances in the environment. Instead of fighting off a disease-causing foreign substance, the immune system launches a complex series of actions against an irritating substance, referred to as an allergen. The immune response may be accompanied by a number of stressful symptoms, ranging from mild to severe to life threatening. In rare cases, an allergic reaction leads to anaphylactic shocka condition characterized by a sudden drop in blood pressure, difficulty in breathing, skin irritation, collapse, and possible death.

The immune system may produce several chemical agents that cause allergic reactions. Some of the main immune system substances responsible for the symptoms of allergy are the histamines that are produced after an exposure to an allergen. Along with other treatments and medicines, the use of antihistamines helps to relieve some of the symptoms of allergy by blocking out histamine receptor sites. The study of allergy medicine includes the identification of the different types of allergy, immunology , and the diagnosis and treatment of allergy.

The most common causes of allergy are pollens that are responsible for seasonal or allergic rhinitis. The popular name for rhinitis, hay fever, a term used since the 1830s, is inaccurate because the condition is not caused by fever and its symptoms do not include fever. Throughout the world during every season, pollens from grasses, trees, and weeds produce allergic reactions like sneezing, runny nose, swollen nasal tissues, headaches, blocked sinuses, and watery, irritated eyes. Of the 46 million allergy sufferers in the United States, about 25 million have rhinitis.

Dust and the house dust mite constitute another major cause of allergies. While the mite itself is too large to be inhaled, its feces are about the size of pollen grains and can lead to allergic rhinitis. Other types of allergy can be traced to the fur of animals and pets, food, drugs, insect bites, and skin contact with chemical substances or odors. In the United States, there are about 12 million people who are allergic to a variety of chemicals. In some cases an allergic reaction to an insect sting or a drug reaction can cause sudden death. Serious asthma attacks are sometimes associated with seasonal rhinitis and other allergies. About nine million people in the United States suffer from asthma.

Some people are allergic to a wide range of allergens, while others are allergic to only a few or none. The reasons for these differences can be found in the makeup of an individual's immune system. The immune system is the body's defense against substances that it recognizes as dangerous to the body. Lymphocytes, a type of white blood cell, fight viruses , bacteria , and other antigens by producing antibodies. When an allergen first enters the body, the lymphocytes produce an antibody called immunoglobulin E (IgE). The IgE antibodies attach to mast cells, large cells that are found in connective tissue and contain histamines along with a number of other chemical substances.

Studies show that allergy sufferers produce an excessive amount of IgE, indicating a hereditary factor for their allergic responses. How individuals adjust over time to allergens in their environments also determines their degree of susceptibility to allergic disorders.

The second time any given allergen enters the body, it becomes attached to the newly formed Y-shaped IgE antibodies. These antibodies, in turn, stimulate the mast cells to discharge its histamines and other anti-allergen substances. There are two types of histamine: H1 and H2. H1 histamines travel to receptor sites located in the nasal passages, respiratory system, and skin, dilating smaller blood vessels and constricting airways. The H2 histamines, which constrict the larger blood vessels, travel to the receptor sites found in the salivary and tear glands and in the stomach's mucosal lining. H2 histamines play a role in stimulating the release of stomach acid, thus contributing to a seasonal stomach ulcer condition.

The simplest form of treatment is the avoidance of the allergic substance, but that is not always possible. In such cases, desensitization to the allergen is sometimes attempted by exposing the patient to slight amounts of the allergen at regular intervals.

Antihistamines, which are now prescribed and sold over the counter as a rhinitis remedy, were discovered in the 1940s. There are a number of different antihistamines, and they either inhibit the production of histamine or block them at receptor sites. After the administration of antihistamines, IgE receptor sites on the mast cells are blocked, thereby preventing the release of the histamines that cause the allergic reactions. The allergens are still there, but the body's "protective" actions are suspended for the period of time that the antihistamines are active. Antihistamines also constrict the smaller blood vessels and capillaries, thereby removing excess fluids. Recent research has identified specific receptor sites on the mast cells for the IgE. This knowledge makes it possible to develop medicines that will be more effective in reducing the symptoms of various allergies.

Corticosteroids are sometimes prescribed to allergy sufferers as anti-inflammatories. Decongestants can also bring relief, but these can be used for a short time only, since their continued use can set up a rebound effect and intensify the allergic reaction.

See also Antibody and antigen; Antibody-antigen, biochemical and molecular reactions; Antibody formation and kinetics; Antigenic mimicry; Immunology

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allergy

allergy, hypersensitive reaction of the body tissues of certain individuals to certain substances that, in similar amounts and circumstances, are innocuous to other persons. Allergens, or allergy-causing substances, can be airborne substances (e.g., pollens, dust, smoke), infectious agents (bacteria, fungi, parasites), foods (strawberries, chocolate, eggs), contactants (poison ivy, chemicals, dyes), or physical agents (light, heat, cold). It is believed that a person who is hereditarily predisposed toward allergy produces, when sensitized, special weak types of antibodies, called reagins, that give little immune protection but cause local tissue damage during the antibody-antigen reaction (see immunity). Allergens can affect the respiratory system, the reaction manifesting itself as asthma or hay fever, or they can affect the skin, causing wheals and rashes. Allergens may also act on the gastrointestinal tract, causing nausea and vomiting. Allergic reactions to substances injected into the bloodstream can cause violent and sometimes fatal reactions (see anaphylaxis; serum sickness). The best treatment of allergic reactions is prevention, i.e., elimination of the offending substances from the sensitive person's environment. If this is not possible, desensitization (i.e., deliberate production of the allergic reaction by injecting the allergen, after which the sufferer is no longer susceptible) is sometimes helpful. Antihistamine drugs may give temporary relief. See histamine.

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Allergies

ALLERGIES

DEFINITION


Allergies are abnormal reactions of the immune system to substances that are otherwise harmless.

DESCRIPTION


Allergies are among the most common medical disorders. By some estimates more than one in every five Americans suffer from some form of allergy. This statistic holds true throughout the world. Allergies are the single most common reason for absence from school, and they are the major cause of hours lost from work.

An allergy is a type of immune reaction. Normally, the immune system protects the body against harmful invaders, like bacteria and viruses. These invaders carry distinctive markers on their outside surface called antigens (pronounced an-TIH-juns). The immune system produces special molecules called antibodies when it finds an antigen. The antibodies attach themselves to the antigens. The antigen-antibody combination sets off a series of changes in the body, which protect the body from infection and disease.

This same sequence of events can also occur with harmless invaders, such as dust and pollen. This response by the immune system is known as an allergy. The markers on the otherwise harmless invaders are known as allergens (pronounced AL-er-jins).

Allergies: Words to Know

Allergen:
A substance that causes an allergic reaction.
Anaphylaxis:
An increased sensitivity to an allergen causing dilation (expansion) of blood vessels and tightening of muscles. Anaphylaxis can result in sharp drops in blood pressure, difficulty in breathing, and death if left untreated.
Antibody:
A chemical produced by the immune system in response to an antigen.
Asthma:
A lung condition in which airways become narrowed, causing wheezing, coughing, and shortness of breath.
Contact dermatitis:
Inflammation of the skin caused by exposure to an allergen.
Histamine:
A chemical released by mast cells that causes cells to become leaky and irritates nerve cells, causing pain.
Mast cells:
A type of cell that makes up the immune system that releases histamine when stimulated by immunoglobin type E, a molecule released by white blood cells.

Allergens can enter the body through four main routes: the nose and mouth, the gastrointestinal (digestive) tract, the skin, and the circulatory (blood) system.

  • Allergens in the air can cause hay fever (see hay fever entry), asthma (pronounced AZ-muh; see asthma entry), or conjunctivitis (pink eye; see conjunctivitis entry).
  • Allergens in food can cause itching and swelling of the lips and throat, cramps, and diarrhea. If they get into the blood, the allergens can cause hives or more serious reactions. Hives are red, itchy blotches on the skin. Food allergens can also cause anaphylaxis (pronounced a-nehfeh-LAK-siss). Anaphylaxis (or anaphylactic shock) is a life-threatening condition in which tissues swell up and begin to close the throat. A person may go into convulsion or a coma.
  • Allergens that come into contact with the skin can cause reddening, itching, and blistering. This condition is called contact dermatitis (pronounced der-muh-TIE-tis). Skin reactions can also occur when allergens enter the body through other routes, such as the mouth or nose.
  • Allergens can enter the body through bites and stings or drug administration (injections or shots). In such cases, the allergens go directly into the bloodstream. They are then carried to other parts of the body where they can exert their effects.

People with allergies are not equally sensitive to all allergens. A person may be allergic to some kinds of food but not affected by breathing in dust or pollen. Sensitivity to allergens can also change over time. A person may become more (or less) allergic to certain allergens as he or she grows older.

CAUSES


When allergens enter the body, they set off a series of reactions. The first of these reactions occurs when the allergens come into contact with lymphocytes (pronounced LIM-fuh-sites), a type of white blood cells. Lymphocytes produce a special kind of marker molecule known as immunoglobulin (pronounced IM-yuh-no-GLOB-yuh-lin) type E (IgE). IgE molecules search out and attach themselves to a second kind of cell, called mast cells.

Mast cells manufacture a chemical known as histamine (pronounced HISS-tuh-meen). When IgE molecules attach themselves to a mast cell, the cell begins to release large amounts of histamine into blood vessels, nerves, and other tissue around it. Histamine causes changes in the cells with which it comes into contact. For example, it causes blood vessels to become leaky. Fluid escapes from the blood vessel, causing swelling and redness in surrounding tissue.

Histamine also causes nerve cells to become more sensitive, producing pain and irritation. All of these changes result in the familiar symptoms of an allergic reaction: redness, swelling, pain, and itching.

Common Allergens

The most common allergens in the air are:

  • Animal fur and dander (dry skin that is shed)
  • Cigarette smoke
  • Dust
  • House mites
  • Mold spores (seeds)
  • Plant pollen
  • Solvents (chemicals used in cleaning)

Common food allergens include:

  • Eggs
  • Fish and shellfish
  • Food additives
  • Milk
  • Nuts, especially peanuts, walnuts, and Brazil nuts
  • Wheat

CAN YOU INHERIT ALLERGIES?

Specific kinds of allergies are not inherited. But the tendency to develop some kinds of allergies can be. This pattern is thought to result from the body's tendency to produce IgE. The more IgE the body produces, the more likely a person is to have allergies. IgE is a hereditary trait. Some people's bodies naturally produce more or less of the chemical, a trait they can pass on to their children.

If neither parent has allergies, the chance of a child developing an allergy is no more than 20 percent. If one parent has allergies, the chance rises to as high as 50 percent. If both parents have allergies, the chance can be as high as 75 percent.

The following types of drugs often cause allergic reactions:

  • Flu vaccines
  • Gamma globulin (pronounced GA-muh GLAH-byu-lun), which are used to treat infectious diseases such as measles (see measles entry) and hepatitis (see hepatitis entry)
  • Penicillin and other antibiotics Common causes of contact dermatitis include the following:
  • Latex products (such as rubber gloves)
  • Nickel or nickel alloys
  • Poison ivy, poison oak, and poison sumac

Insects or other animals whose bites or stings can cause allergies include the following:

  • Bees, wasps, hornets, and yellow jackets
  • Fleas
  • Mosquitoes

SYMPTOMS


Symptoms depend on the specific kind of allergic reaction. Allergens in the air can cause an itchy, runny nose with post-nasal drip. Post-nasal drip occurs when fluid runs out of the back of the nose into the throat. When this happens, the throat can become scratchy and irritated. The thin membrane around the eye can also become irritated by allergens in the air. When this happens, the eye becomes red and itchy and begins to produce tears. Severe reaction to allergies may cause a disease called asthma. The symptoms of asthma include wheezing, coughing, and shortness of breath.

Food allergens can cause a variety of symptoms depending on a person's sensitivity to the allergen and the part of the body to which it goes. In the mouth and throat, an allergen can cause swelling and tingling in the lips, tongue, or throat. In the stomach, it can cause nausea, cramps, and diarrhea.

Contact dermatitis is marked by red, itchy skin that may develop skin blisters that ooze fluid.

Allergic reactions that spread throughout the body can occur with any kind of allergen. They tend to be more common, however, with allergens that enter the bloodstream through an insect bite or injection. Anaphylaxis is one of the most dangerous of these reactions.

DIAGNOSIS


Diagnosis of allergies usually occurs in two steps. First, a doctor takes a medical history of the patient. He or she tries to find some connection between an allergic reaction and a particular allergen, such as a specific food or insect bite.

Second, direct tests can be carried out to discover the allergens to which a patient might be sensitive. In skin patch tests, for example, small amounts of many different allergens are placed directly on a person's skin. Any reaction that occurs to an allergen indicates that the person is allergic to that allergen.

TREATMENT


A large number of prescription and over-the-counter drugs are available for treating allergic reactions. Most of these work by interfering with the action of histamine on cells. Other drugs counteract the effects of histamine. They stimulate other systems or reduce immune responses in general.

Antihistamines

Antihistamines prevent histamine from exerting its effect on nasal (nose) cells. They can be used after an allergic reaction has begun. But they are more effective if used preventively, before symptoms appear. Many people take an antihistamine every day, whether they feel uncomfortable or not.

A wide variety of antihistamines is available. They are among the most widely sold of all drugs. Older types of antihistamines often caused drowsiness as a side effect. Included among these drugs are diphenhydramine (pronounced DIE-fen-HI-druh-meen, trade name Benadryl), chlorpheniramine (pronounced KLOR-fen-er-uh-meen, trade name Chlor-trimeton), brompheniramine (pronounced BROM-fen-er-uh-meen, trade name Dimetane), and clemastine (pronounced KLEM-uh-steen, trade name Tavist).

Newer antihistamines do not cause drowsiness. They are available by prescription and include drugs such as astemizole (pronounced a-STEM-uh-zole, trade name Hismanal), loratadine (luh-RAT-uh-deen, trade name Claritin), and fexofenadine (pronounced fex-o-FEN-uh-deen, trade name Allegra). One of the most popular antihistamines was terfenadine (pronounced tir-FEN-uh-deen, trade name Seldane), the original nondrowsiness medication. It was taken off the market by its manufacturers in 1998 because questions about its safety had arisen. In addition, a safer alternative, fexofenadine, had become available.

Decongestants

Decongestants have the opposite reaction on blood vessels from that of histamines. They cause the blood vessels to constrict and hold fluid better. Therefore, they reduce the swelling, itchiness, and redness usually caused by histamine.

Decongestants can be taken in the form of nasal sprays or pills. They should be used with caution as they can produce side effects such as headaches, increased blood pressure and heart rate, and agitation. If used for too long a period of time, they can also cause a rebound effect. In a rebound effect, the nasal passages become even more swollen and tender than they were originally.

Topical Corticosteroids

Topical corticosteroids (pronounced KOR-ti-ko-steer-oids) are drugs used directly on the skin that reduce inflammation of mucous membranes, the tissues that line the nose, mouth, and other body openings. Topical corticosteroids tend to work more slowly and last longer than other allergy medications. A person generally starts to apply these drugs before an allergic reaction (such as hay fever) begins. The drugs can provide an extended period of protection, throughout the period during which the allergen is present.

Mast Cell Stabilizers

Mast cell stabilizers prevent mast cells from releasing histamine, which means they prevent the symptoms of allergies from developing. The most common mast cell stabilizer is cromolyn (pronounced KRO-muh-lun) sodium. The drug is often taken year-round in the form of a nose or throat spray.

Immunotherapy

Immunotherapy is also known as desensitization. This treatment takes the form of a series of injections (shots) taken over long periods of times (months or years). The shots contain a chemical that reduces the ability of IgE to cause allergic reactions. The amount of this chemical in the injection is gradually increased over time.

The effects of immunotherapy often do not show up for long periods of time. With about 20 percent of all patients, they are never very effective. The most serious possible side effect of a desensitization injection is anaphylactic shock.

Bronchodilators

Allergic reactions in the lungs cause airways to tighten, which makes it difficult for a person to breathe. Bronchodilators (pronounced brong-ko-die-LATE-urs) are substances that reverse this action. They cause air passages to dilate, or become more open, so that air flows more easily through them.

Bronchodilators are commonly used in serious asthma attacks. They are administered through nose or throat sprays. In the most serious cases, these drugs can be injected directly into the bloodstream. Some commonly used bronchodilators are adrenaline (pronounced uh-DREN-uh-lin), albuterol (pronounced al-BYOO-tuh-rol), various steroids, and theophylline (pronounced thee-OFF-uh-lin), a component of coffee and tea.

Treatment of Contact Dermatitis

Calamine lotion and corticosteroid creams can reduce the discomfort and itching of contact dermatitis. Overuse of corticosteroids can, however, lead to dry and scaly skin.

Treatment of Anaphylaxis

Anaphylaxis is one of the most serious conditions relating to allergic reactions. A person who goes into anaphylactic shock must be treated very quickly or he or she may die. The standard treatment for anaphylaxis is an injection of adrenalin, also known as epinephrine (pronounced EP-uh-nefrin). People who are at risk for anaphylaxis often carry with them an Epipen, a small needle containing a dose of adrenalin.

Alternative Treatment

The most effective alternative to medical treatment for allergies is to avoid the allergens that cause them. A person who is allergic to peanuts, for example, should avoid eating peanuts or foods that contain them.

In addition, a number of natural products have been found to be effective in treating allergic reactions. Products that have been suggested as alternatives for each of the medical treatments that have been discussed include:

  • Antihistamines: Vitamin C and the natural product known as hesperidin (pronounced he-SPER-i-din).
  • Decongestants: Vitamin C, the amino acid N-acetylcysteine (pronounced uh-seet-uhl-SIS-tuh-een), and the minerals iron phosphate and potassium chloride.
  • Mast cell stabilizers: The natural products hesperidin and quercetin (pronounced KWER-si-tin).
  • Immunotherapy: The herbs echinacea (ek-i-NAY-see-uh) and milk-vetch root (astragalus, pronounced uh-STRAG-uh-luhs).
  • Bronchodilators: The herbs ephedra (pronounced i-FED-ruh), khellin (pronounced KEL-un), and cramp bark.

Alternative Treatment of Contact Dermatitis

The use of certain herbs taken internally or applied directly to the skin has been recommended as a treatment for the pain and itching of contact dermatitis. One treatment consists of a paste containing jewelweed or chickweed applied to the skin. A cream containing calendula (pronounced KUH-len-juh-luh) sometimes relieves a rash. The use of certain drinks or pills made of herbs may also be effective against contact dermatitis.

PROGNOSIS


Some allergies become less severe over time, while others become more serious. Anaphylaxis and asthma are the most serious problems associated with allergies. Either can result in death if not properly treated.

PREVENTION


The best approach for dealing with allergies is to find out which allergens cause sensitivity and then avoid them to the greatest extent possible. If one is allergic to certain foods, for example, those foods must be avoided. Allergens carried through the air can be the most difficult to avoid. The best approach is to keep a house as clean as possible, to avoid animals that cause allergic reactions, and to be aware of other housekeeping activities that will reduce the number of allergens to which one is exposed.

See also: Hay fever.

FOR MORE INFORMATION


Books

Novick, N. L. You Can Do Something about Your Allergies. New York: Macmillan, 1994.

Weil, A. Natural Health, Natural Medicine: A Comprehensive Manual for Wellness and Self-Care. Boston: Houghton Mifflin, 1995.

Organizations

American Academy of Allergy, Asthma, and Immunology. (800) 8222762. http://www.aaaai.org.

National Institute of Allergy and Infectious Diseases. Building 31, Room 7A-50, 31 Center Drive, MSC 2520, Bethesda, MD 208922520. http://www.niaid.nih.gov.

Web sites

The On-Line Allergy Center. [Online] http://www.onlineallergycenter.com (accessed on October 5, 1999).

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Allergies

Allergies

The Immune System

What Are Allergies?

How Do Antibodies Cause Allergy Symptoms?

What Kinds of Allergies Do People Have?

How Do Doctors Diagnose Allergies?

How Do Doctors Treat Allergies?

Living with Allergies

Resources

Allergies are abnormally sensitive reactions to usually harmless substances in the air people breathe, the things they touch, or the foods they eat.

KEYWORDS

for searching the Internet and other reference sources

Antibodies

Antigens

Immunotherapy

The Immune System

The human body is filled with special cells and organs that stand ready to fight invaders. Together they are called the immune system.

Antibodies

One line of defense in the immune system is a protein called an antibody. These antibodies are like the hall monitors of the bloodstream, constantly looking around for troublemakers. When they spot a troublemaker, the antibody grabs it to make sure it does not cause problems and then removes it. Antibodies are an important way the body fights infections, colds, viruses, and diseases. Antibodies roam through the bloodstream and look for foreign substances that are not supposed to be there.

Antigens

Foreign substances in the body are called antigens. Usually, antigens are things we want removed, like a virus. Sometimes, however, the antibodies attack a usually harmless substance that in most people would not cause the immune system to swing into action. There are hundreds of substances in the air people breathe, the food they eat, and the things they touch that may cause this reaction. When it occurs, people are said to have allergies. It is a disorder than affects more than 50 million Americans.

What Are Allergies?

When Latrell plays outside during some months of the year, he sneezes and his throat feels itchy. When Melinda visits an apartment where there is a cat, she finds her eyes start to water. When Mrs. Gonzalez feeds her baby formula with a milk product, the baby cries and seems to have a stomach ache. And when Bobby touches anything with metals like chrome, his skin develops hives.

All of these are examples of allergic reactions. Most people can play outside, pet animals, drink milk, and touch metals without any problems. But for millions of people with allergies, these things and hundreds more can cause their bodies immune systems to jump into action. Their reactions can be as mild as a stuffy nose or as severe as death.

People can be allergic to many things, but most allergies fall into four main categories:

  • Things that are inhaled, such as pollen, dust, mold spores, and pet dander*.
* pet dander
refers to microscopic parts of the pets skin that flake off and get into the air people breathe.
  • Things that are eaten, such as milk and items made with milk; eggs; shellfish like shrimp; and peanuts and other nuts.
  • Things that are injected, such as penicillin and some other medications, or the venom from an insect sting.

Things that are touched, such as nickel in costume jewelry, dyes in nail polish and shampoos, and latex*.

* latex
(LAY-tex) is a substance made from a rubber tree and is used in such things as medical equipment (especially gloves), toys, and other household products.

How Do Antibodies Cause Allergy Symptoms?

The first time the bodys immune system is confronted with a foreign substance like a virus, it remembers the substance. This allows the bodys immune system to disarm the foreign substance with antibodies the next time it is encountered.

Allergy Rates and Lifestyles

In the 1960s, about 3 percent of American children had allergic dermatitis, or allergic reactions to things they touched. By the late 1990s, that number had increased to 10 percent. The numbers are similar or even higher for asthma and other allergic disorders. Why the increase?

The American Academy of Allergy, Asthma and Immunology suggests several reasons, ranging from differences in how bodies are functioning, to changes in lifestyle and the environment, to better reporting and diagnoses of allergies.

Lifestyle factors that may influence allergy rates:

  • People are living in houses and working in offices that are better insulated than in the past, and they are spending more time in them. This puts them in contact more often with dust mites and other pollutants that cause allergies.
  • Poverty also appears to be a factor. Increasing numbers of poor people have asthma, and often cannot get the medical care they need.

The body can produce millions of different antibodies. Their job is to capture the foreign substance by binding onto it, like two puzzle pieces fitting together. These antibodies are also called immunoglobulins (im-mune-o-GLOB-u-linz).

IgE

An antibody known as immunoglobulin gamma E (IgE) causes allergic reactions by attacking substances that are foreign, but which usually are harmless to most people, like pollen, food, and metals. When IgE attacks, it causes special cells known as mast cells to release chemicals that irritate people with allergies.

Mast cells

Mast cells are found in large quantities in places like the nose, eyes, lungs, stomach, and intestines. As mast cells release irritating chemicals, the tissues swell and produce the other symptoms of inflammation and allergies.

But why do everyday substances like food cause allergic reactions in some people and not others? Scientists believe the tendency may be something inherited from parents. Other possible reasons range from lifestyle to changes in the environment.

What Kinds of Allergies Do People Have?

Many people have more than one thing that causes their allergies.

Allergic rhinitis

The most common allergy is allergic rhinitis (ry-NITE-is), which is commonly known as hay fever. It affects about 35 million people in the United States, many of whom are allergic to pollen and mold spores from plants and trees. Allergic rhinitis causes a runny nose, sneezing, and itchy nose and throat.

Skin allergy

Another common problem is skin allergy, whose medical name is allergic dermatitis. Hundreds of substances in metals, cosmetics, shampoos, some medications, and other chemicals can cause an allergic reaction when some people come into contact with them. It causes the skin to itch and develop a rash. About 10 percent of children have allergic dermatitis.

Latex allergy

Recently, there has been a lot of interest in allergic reactions to natural latex rubber, which is used in many medical devices, toys, and other things around the house. A latex allergy can cause symptoms like allergic dermatitis, but it also can cause anaphylaxis, the most dangerous allergic reaction, which can cause death unless people are treated quickly.

Insect Stings Insect stings can trigger an allergic reaction, including anaphylaxis. The stings can cause minor reactions in most people, like pain, swelling, and itching around the sting. But for some, the sting causes an allergic reaction throughout the body.

Anaphylaxis and Epinephrine

Anaphylaxis is the most dangerous allergic reaction, and it can cause death unless people are treated quickly.

Unlike other allergic reactions that usually affect just the nose, skin, or stomach, anaphylaxis affects many parts of the body. Anaphylactic shock is a medical emergency: the throat and airways to the lungs may swell, causing trouble with breathing. Blood pressure may drop, and people may feel nauseated and have diarrhea and stomach cramps. Without immediate medical treatment, people with anaphylactic shock may lose consciousness and die.

Like all allergies, anaphylaxis results from an abnormal reaction to something that does not cause trouble for most people. People cannot know they are at risk of anaphylaxis until they are exposed more than once to an insect sting, food, or other substance. Common triggers include:

  • Insect stings, with as many people as 5 percent of the population at risk of anaphylaxis from stings from bees, wasps, or fire ants. About 40 deaths a year result from such stings in the U.S.
  • Medications, especially penicillin.
  • Foods, especially peanuts, shellfish, and some food additives.
  • Latex.

The best prevention is avoiding situations and substances that can cause the reaction.

The most common treatment is epinephrine (ep-i-NEF-rin), also known as adrenaline. People who have had anaphylactic shock often carry epinephrine, which can be injected with a needle.

Food allergies

Reactions to certain specific foods also are common. When some people eat foods like eggs, milk, shellfish, or peanuts, they experience an allergic reaction. It can manifest as itching in the mouth and throat, hives, stomach cramps, nausea, vomiting, or diarrhea.

Asthma

Certain foods as well as allergens that are inhaled also contribute to asthma, a chronic lung disease that affects up to 17 million Americans.

How Do Doctors Diagnose Allergies?

The symptoms of allergies are varied and similar to the symptoms of other disorders. For example, a runny nose could signal allergic rhinitis, a cold, or influenza. Diarrhea could mean a food allergy or food poisoning from bacteria in contaminated food.

This can make it difficult for doctors to diagnose allergies. The first thing doctors usually do is take the medical history of both the person with the possible allergy and the history of family members. Doctors are looking for the situations where the allergic reactions occur and whether other family members have a history of allergies, since they tend to run in families. They also want to rule out other possible causes of the reaction.

Doctors may use an allergy skin test. This involves placing a small amount of various substances on the skin to see if any of them cause an allergic reaction. Or the doctors may test the blood for the presence of IgE, the antibody that exists in higher levels in people with allergies than in people without them.

If doctors suspect the allergy is to a particular food or material (like dairy products or latex), they usually try to have patients avoid them and see if the symptoms get better.

How Do Doctors Treat Allergies?

Avoiding allergens

Once doctors determine that patients have an allergy, the first line of defense is avoiding the substance as much as possible. In some cases, that can be relatively easy, such as if people are allergic to a particular food, like nuts, milk, or shrimp, or to a substance, like nickel or chrome. Allergies to pet dander can be limited by not having animals in the home and by avoiding them in other places.

It gets more difficult to avoid substances like pollen, mold spores, and dust mites*. But even these things can be avoided to some extent. For example, people can stay indoors more or close their windows during times when pollen and mold spores are high in their areas. And dust mites can be controlled by removing rugs, or by vacuuming rugs often, by covering pillows and mattresses with protective material, by washing sheets regularly in hot water, and by using special filters on heaters and air conditioners.

* dust mites
are tiny insects that live in dust and in materials like carpets, pillows, mattresses and furniture.

Antihistamines and decongestants

There are many over-the-counter and prescription medications for allergy. Some people take them only when symptoms occur. Others use them daily to prevent allergy symptoms or at least to make them less severe. Histamine is one of the chemicals released in mast cells when people have allergic reactions. Antihistamine medications help neutralize the chemical. Often antihistamines are taken with a decongestant, which helps open nasal passages. Some antihistamines cause drowsiness, although newer versions do not cause as much sleepiness as older ones.

Medic Alert Tags

Medic Alert tags and bracelets are useful for people with drug allergies. Wearing the tag or bracelet can alert medical personnel to the allergy in the event of an accident or loss of consciousness.

Some companies offer medical alert tags that have an identification number that is unique for the individual. In the event of an accident, a doctor anywhere could retrieve the patients medical history.

Peanut-Free Zones

Some schools have discussed the need for a peanut-free zone, which would be an area where no peanut or peanut products could be served or eaten. It sounds odd, but the schools are reacting to increasing reports of a dangerous allergy to a lunchroom staple, peanut butter, as well as to other foods made with peanuts.

Peanuts and other nuts are among the most common foods that cause allergic reactions, and the reaction can be particularly dangerous if it causes anaphylaxis. Experts estimate that more people die each year from allergic reactions to peanuts than from bee stings.

People with peanut allergy can react to very small amounts; some may react just from smelling peanuts. Because such small amounts of peanuts can trigger an allergic reaction, some schools have removed peanut butter and similar foods from their menus.

As children grow, they sometimes find that their allergies get better. Until then, it is important to avoid things that cause allergic reactions and, for food allergies, always to read food labels carefully. Food manufacturers sometimes change ingredients, so even familiar foods and familiar brand names may not remain peanut free.

Another alternative for people with allergic rhinitis are sprays that are used in the nose. Some of these help reduce swelling in the nose, and others work to prevent mast cells from releasing their chemicals. Some of these are available without a prescription and others require a prescription.

Immunotherapy

For some patients, doctors suggest immunotherapy, which commonly involves allergy shots. By injecting a small amount of an allergen into patients, immunotherapy aims to help the body become less sensitive by regularly exposing it to the substances that cause the allergic reaction. Immunotherapy is used for people who are allergic to substances like pollen, dust mites, and animal dander, but not for people allergic to foods. The shots are given as often as several times a week at first and then reduced to about once a month for three to five years afterward.

Living with Allergies

Allergies can be anything from an annoyance to a life-threatening illness. Most people, however, can find ways to live with their allergies by avoiding those things that cause them, and by seeking treatment when necessary.

See also

Asthma

Hives

Skin Conditions

Resources

Books

The American Lung Association Asthma Advisory Group, with Norman H. Edelman, M.D. Family Guide to Asthma and Allergies: How You and Your Children Can Breathe Easier. Boston: Little Brown, 1998.

Pressman, Alan, Herbert D. Goodman, and Rachelle Bernadette Nones. Treating Asthma, Allergies and Food Sensitivities (Physicians Guide to Healing). New York: Berkley, 1997.

Organizations

U.S. National Institute of Allergy and Infectious Diseases, Office of Communications and Public Liaison, Building 31, Room 7A-50, 31 Center Drive MSC 2520, Bethesda, MD 20892-2520. http://www.niaid.nih.gov/

American Academy of Allergy, Asthma and Immunology, 611 East Wells Street, Milwaukee, WI 53202. http://www.aaaai.org/

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allergy

allergy A condition in which the body produces an abnormal immune response to certain antigens (called allergens), which include dust, pollen, certain foods and drugs, or fur. In allergic individuals these substances, which in a normal person would be destroyed by antibodies, stimulate the release of histamine and serotonin, leading to inflammation and other characteristic symptoms of the allergy (e.g. asthma or hay fever). This response is a type of hypersensitivity. See also anaphylaxis; mast cell.

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allergy

allergy (al-er-ji) n. a disorder in which the body becomes hypersensitive to particular antigens (called allergens), which provoke characteristic symptoms whenever they are subsequently encountered. Different allergies afflict different tissues and may have either local or general effects, varying from asthma and hay fever to severe dermatitis or gastroenteritis or extremely serious shock (see anaphylaxis).
allergic adj.

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allergy

allergy Disorder in which the body mounts a hypersensitive reaction to one or more substances (allergens) not normally considered harmful. Typical allergic reactions are sneezing (hay fever), “wheezing” and difficulty in breathing (asthma) and skin eruptions and itching (eczema). A tendency to allergic reactions is often hereditary.

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allergic

al·ler·gic / əˈlərjik/ • adj. caused by or relating to an allergy: an allergic reaction. ∎  having an allergy to (a substance): allergic to the sting of bees. ∎  (allergic to) inf. having a strong dislike for: I'm allergic to the hype.

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allergy

al·ler·gy / ˈalərjē/ • n. (pl. -gies) a damaging immune response by the body to a substance, esp. pollen, fur, a particular food, or dust, to which it has become hypersensitive. ∎ inf. an antipathy: their allergy to free enterprise.

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allergy

allergy XX. — G. allergie. f. Gr. állos other, ALLO- + érgon work + -Y2 (cf. ENERGY).
Hence allergic XX.

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allergy

allergy Adverse reaction to foods caused by the production of antibodies.

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allergic

allergicbathypelagic, magic, tragic •neuralgic, nostalgic •lethargic, Tajik •Belgic •paraplegic, quadriplegic, strategic •dialogic, ethnologic, hydrologic, isagogic, logic, monologic, mythologic, pathologic, pedagogic, teleologic •georgic • muzhik •allergic, dramaturgic •anarchic, heptarchic, hierarchic, monarchic, oligarchic •psychic • sidekick • dropkick •synecdochic • Turkic •Alec, cephalic, encephalic, Gallic, intervallic, italic, medallic, mesocephalic, metallic, phallic, Salic, tantalic, Uralic, Vandalic •catlick • garlic •angelic, archangelic, evangelic, melic, melick, philatelic, psychedelic, relic •Ehrlich • Gaelic •acrylic, bibliophilic, Cyrillic, dactylic, exilic, idyllic, imbecilic, necrophilic •niblick • skinflick •acyclic, cyclic, polycyclic •alcoholic, anabolic, apostolic, bucolic, carbolic, chocoholic, colic, diabolic, embolic, frolic, hydraulic, hyperbolic, melancholic, metabolic, parabolic, rollick, shambolic, shopaholic, symbolic, vitriolic, workaholic •saltlick • cowlick • souslik • gemütlich •public • Catholic

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allergy

allergy •haji • algae • Angie •argy-bargy, Panaji •edgy, sedgy, solfeggi, veggie, wedgie •cagey, stagy •mangy, rangy •Fiji, gee-gee, squeegee •Murrumbidgee, ridgy, squidgy •dingy, fringy, mingy, stingy, whingy •cabbagy • prodigy • effigy • villagey •porridgy • strategy • cottagey •dodgy, podgy, splodgy, stodgy •pedagogy •Georgie, orgy •ogee • Fuji •bhaji, budgie, pudgy, sludgy, smudgy •bulgy •bungee, grungy, gungy, scungy, spongy •allergy, analogy, genealogy, hypallage, metallurgy, mineralogy, tetralogy •elegy •antilogy, trilogy •aetiology (US etiology), amphibology, anthology, anthropology, apology, archaeology (US archeology), astrology, biology, campanology, cardiology, chronology, climatology, cosmology, craniology, criminology, dermatology, ecology, embryology, entomology, epidemiology, etymology, geology, gynaecology (US gynecology), haematology (US hematology), hagiology, horology, hydrology, iconology, ideology, immunology, iridology, kidology, meteorology, methodology, musicology, mythology, necrology, neurology, numerology, oncology, ontology, ophthalmology, ornithology, parasitology, pathology, pharmacology, phraseology, phrenology, physiology, psychology, radiology, reflexology, scatology, Scientology, seismology, semiology, sociology, symbology, tautology, technology, terminology, theology, topology, toxicology, urology, zoology • eulogy • energy • synergy • apogee • liturgy • lethargy •burgee, clergy •zymurgy • dramaturgy

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