Dermatitis is the general medical term for inflammation of the skin. It includes a broad range of rashes, ranging from atopic dermatitis (eczema) to sunburn and various types of skin infections.
There are five basic types of dermatitis:
- Atopic dermatitis (AD). Characterized by itching, scaling, and swelling rash on the skin that may form oozing open sores or yellow and red pimples, the rash is most likely to affect the skin of the hands and feet, the arms, the area behind the knees, and the ankles, wrists, face, neck, and upper chest.
- Contact dermatitis. Rashes caused by touching a foreign substance. There are two major forms of contact dermatitis: allergic, caused by contact with a plant or animal substance that a person has become sensitized to; and irritant, caused by touching something that damages the skin directly. Poison ivy is an example of an allergic contact dermatitis; rashes caused by detergents or other household chemicals are examples of irritant contact dermatitis.
- Cercarial dermatitis. Commonly known as swimmer's itch, it is caused by certain parasites that live in ducks, geese, and freshwater snails. (A parasite is an organism that lives off another, larger, organism.) When a person swims in water containing these parasites, they can burrow into the skin and cause a short-lived itchy
rash with small reddish pimples or blisters. It mostly affects the parts of the body that are not covered by a swimsuit, and does not usually affect the face, palms of the hands, or soles of the feet.
- Radiation dermatitis. The most common form of radiation dermatitis is photodermatitis or sunburn. It is characterized by redness, pain, and swelling of the affected skin following exposure to sunlight or a tanning lamp. Severe sunburn includes the formation of blisters and peeling of the affected skin, which usually begins to peel about three days after exposure and may continue for another week or so. A rarer form of radiation dermatitis, found mostly among hospital staff, is caused by repeated exposure to x-ray and other imaging equipment in hospitals.
- Seborrheic dermatitis. Found on the scalp and other areas of the face and chest that contain oil-secreting glands, it is characterized by a reddish, greasy-looking rash on the skin and oily flakes of skin. In infants, it is called cradle cap. In adults, the most common form of seborrheic dermatitis is dandruff.
The demographics of dermatitis depend on the type:
- Atopic dermatitis. AD is more common among children than adults; 95 percent of cases occur in children five years or younger. About 15 million people in the United States have some form of eczema. The rate in adults is about 0.9 percent. AD is slightly more common in women than in men.
- Contact dermatitis. Contact dermatitis is common in the general population, affecting fourteen people per 1,000; one health survey estimated that about 9 million visits to doctors every year are for contact dermatitis. Contact dermatitis accounts for about 9 percent
of all visits to dermatologists in the United States. Women appear to be more likely to report contact dermatitis than men.
- Cercarial dermatitis. Cercarial dermatitis can affect anyone who swims in contaminated water; however, children are more likely than adults to develop swimmer's itch because they are more likely to wade or swim in shallow water and less likely to towel dry or rinse off after swimming.
- Radiation dermatitis. Sunburn is very common in the general population in North America. According to Skin Cancer Foundation survey, 42 percent of people reported getting sunburned at least once in the preceding year. Radiation dermatitis caused by exposure to imaging equipment is now quite rare among hospital workers because the long-term impact of radiation on skin is now better understood.
- Seborrheic dermatitis. Dandruff, the mildest form of this dermatitis, is estimated to affect about 15–20 percent of adults in the United States. It is most common in people from the late teens to the late forties, and affects men somewhat more often than women. It appears to be equally common in all races and ethnic groups.
When to See the Doctor
Most cases of sore or irritated skin are not medical emergencies and do not require specialized treatment. People with the following symptoms, however, should see a dermatologist quickly because they may be early signs of skin cancer:
- A growth on the skin that was not there before the rash or sunburn.
- A sore that bleeds, crusts over, keeps reopening, and does not heal within two weeks.
- A change in the size, color, or texture of a mole.
- A dark flat spot on the skin that is gradually enlarging.
The causes of dermatitis vary:
- Atopic dermatitis. Most doctors think that AD results from an immune overreaction inside the body that leads to inflammation and cracked, itchy skin. The breaks in the skin then let in more allergens, irritants, and microbes that made the skin itch and burn even more. A more recent theory holds that some cases of AD are caused by a defective gene for filaggrin, a protein in the skin that normally holds in moisture.
- Contact dermatitis. Contact dermatitis can be caused by a wide range of allergens and irritants. Allergens may include rubber; the nickel and other metals used in jewelry; perfume and perfumed
soaps and creams; hair dye and cosmetics; poison ivy and poison sumac; and neomycin, a common ingredient in topical antibiotic creams. Common irritants include laundry soap, skin soaps, dishwashing detergents, silver polish, shower cleaners, household ammonia, and similar products.
- Cercarial dermatitis. Cercarial dermatitis is caused by parasites that spend part of their life cycle in the water in ponds, small streams, and along shorelines. Swimmer's itch usually appears within four to forty-eight hours of exposure to water containing the parasites.
- Radiation dermatitis. Sunburn is caused by ultraviolet (UV) radiation from the sun or a tanning lamp. In rare cases it is caused by occupational exposure to x-ray and other medical imaging equipment.
- Seborrheic dermatitis. The causes of seborrheic dermatitis are not completely understood. It is thought to result from an overreaction of the person's immune system to a fungus that lives on the scalp. Emotional stress or changes in the seasons may cause flare-ups.
A primary care doctor will usually base the diagnosis by looking at the patient's skin, together with taking a personal and family history of allergies, hay fever, and skin disorders. The patient may be referred to a dermatologist (a doctor who specializes in disorders of the skin) to rule out the possibility that the rash or skin irritation is caused by other diseases. The dermatologist may take a skin biopsy in order to exclude other causes.
Swimmer's itch can be a challenge to diagnose because there are no tests specific for the parasites that cause it, and the rash looks a lot like poison ivy or chickenpox. In many cases the only clue is that the patient went swimming within the past few days.
For contact dermatitis, the doctor may perform a patch test in order to identify the specific substance(s) causing the rash. Small quantities of suspected allergens or irritants in individual containers or patches are applied to the skin of the patient's back. The patches are covered with special nonallergenic adhesive tape for forty-eight hours and then removed; the patient's skin is examined for blisters, swelling, or other reactions to the substances in the patches.
Treatment for dermatitis depends on the cause of the skin rash:
- Atopic dermatitis. Treatment focuses on reducing the itching (and therefore scratching) of the rash; lowering inflammation; and preventing flare-ups. Medications include moisturizers, steroid medications, antihistamines, and drugs that affect the functioning of the immune system.
- Contact dermatitis. Mild contact dermatitis is treated with creams containing cortisone that are applied directly to the rash or with antihistamines taken by mouth. Wet compresses may also help to relieve the itching. Severe cases of contact dermatitis may require oral or injected steroid medications or antibiotics.
- Cercarial dermatitis. Swimmer's itch does not usually require a visit to the doctor. It can be treated at home with over-the-counter antihistamines, calamine lotion, or cortisone cream to relieve the itching. Bathing in water containing baking soda or an oatmeal treatment like Aveeno may also help. If the itching is severe, the doctor may order a prescription-strength cream or lotion.
- Radiation dermatitis. Most mild cases of sunburn eventually heal without special attention from a doctor. Home care may include bathing in cool (not cold) water with baking soda added to the bath water; applying aloe vera gel or other non-greasy moisturizing lotion; and taking a nonaspirin pain reliever.
- Seborrheic dermatitis. Seborrheic dermatitis of the face or chest may be treated with antibiotic, antifungal, or steroid creams applied directly to affected areas. For dandruff, the doctor will usually recommend special shampoos containing salicylic acid, tar, selenium, sulfur, or zinc, and advise the patient to wash the hair more frequently and leave the shampoo on the scalp for about five minutes.
The prognosis depends on the type of dermatitis:
- Atopic dermatitis. About half of children diagnosed with AD will improve by age fifteen; the other half will have lifelong symptoms. It is unusual for a person to develop eczema for the first time after age thirty unless they are working in a harsh climate or a wet environment.
- Contact dermatitis. Even without medical treatment most cases improve within a few days to three to four weeks after exposure to the allergen or irritant has stopped.
- Cercarial dermatitis. Most cases clear up by themselves in a few days to a week without medical treatment, although home treatment with calamine or antihistamines will relieve the itching more rapidly.
- Radiation dermatitis. Most mild cases of sunburn heal without problems in the short term. Blisters that become infected usually heal completely once the infection is treated. The long-term prognosis is of greater concern, as a history of repeated sunburn increases a person's risk of melanoma (the most serious form of skin cancer).
- Seborrheic dermatitis. There is no long-term cure for this type of dermatitis; however, faithful use of the shampoos and skin treatments prescribed by the doctor usually relieves symptoms and lowers the risk of flare-ups.
Prevention of most forms of dermatitis consists of first identifying and then avoiding the allergen or other cause of the skin rash:
- Atopic dermatitis. Prevention of AD consists of identifying the specific substances that trigger skin reactions; avoiding contact with them whenever possible; and applying products that relieve the itching, dryness, and inflammation of the skin.
- Contact dermatitis. In addition to advising the patient to avoid the allergen or irritating substance, in some cases the doctor can recommend substitutes for the specific products or substances causing the rash.
- Cercarial dermatitis. To prevent swimmer's itch, people should choose swimming areas carefully; avoid marshy or shoreline areas where snails often live; rinse off thoroughly after swimming; and use chlorine to keep home pools free of parasites.
- Radiation dermatitis. Staying out of the sun between 10 a.m. and 4 p.m.; wearing a hat and clothing that covers as much of the body as possible; and using sunscreen when outdoors.
- Seborrheic dermatitis. Avoiding the use of hair spray or greasy hair gels or creams is usually necessary. Stress management techniques are helpful to some patients in preventing flare-ups caused by emotional stress.
Dermatitis is likely to continue to be a commonplace health problem, if only because it has so many forms and causes.
SEE ALSO Eczema; Hives; Sunburn
WORDS TO KNOW
Allergen: Any substance that can provoke an allergic reaction in susceptible individuals.
Contact dermatitis: Inflammation of the skin caused by direct contact with an allergen or irritating substance, such as poison ivy, certain dyes, or certain metals.
Dermatologist: A doctor who specializes in diagnosing and treating diseases of the skin.
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