Poison Ivy, Oak, and Sumac
Poison ivy, oak, and sumac
Poison ivy, oak, and sumac are allergic skin rashes (or Rhus dermatitis ) caused by the plants of the same name. All three plants secrete a potent, irritating oil known as urushiol that causes blistering and intense itching once it penetrates the skin.
The allergic rash of poison ivy, oak, and sumac is characterized by red, weeping blisters and severe itching. The rash usually appears within one to two days of initial contact with the plant oil, although it may take longer to appear in areas where the skin is thicker, and lasts from one to three weeks (longer in severe cases). It starts as itchy, inflamed red patches or streaks, and as the oil penetrates into the skin, blisters and small papules form.
Poison plant rash cannot be spread from person to person by contact with the rash itself or fluid from the blisters, and scratching does not spread the rash (although it can cause scarring and potential infection). Only urushiol oil can cause the rash.
Urushiol oil or resin is found in the leaves, roots, and woody parts (i.e., vines and stems) of the poison ivy, oak, and sumac plants. It is a clear substance that is released by the plant when it is cut or bruised. Leaves are bruised easily, especially in the spring, so even a gentle brush against a plant can cause the urushiol to seep out and onto the skin.
Urushiol can remain active for years. For that reason, even dead poison ivy, oak, or sumac plants must be handled with care. Plants should never be burned or shredded, as airborne particles can spread the oil to sensitive areas like the face and eyes and may potentially cause damage to lungs.
The three main sources of poison plant rash—poison ivy, poison oak, and poison sumac—are members of the Anacardiaceae, or cashew, family. While they are usually concentrated most heavily in a few specific regions of the country, all three have been found in locations throughout the United States. Identifying the plant, particularly if people live in a wooded area or have a lot of vegetation in their yards or neighborhood, is essential to preventing the rash.
Poison ivy, known as Rhus radicans or Toxicondendron radicans, is found throughout the United States. The plant grows in vines (typical in the Midwest, East coast, and South) or small bushes (in the North, West, and Great Lakes region), and has clusters of three leaves. (Hence the popular saying: "Leaves of three, let them be.") The leaves are red in the spring; green throughout the summer; and yellow, red, and orange in the fall when they also produce white berries.
Poison oak is a small shrub. The plant, which is also known as Rhus diversiloba or Toxicondendron diversilobum, is found in the western United States. Like poison ivy, poison oak leaves change color with the seasons. The plant also produces white berries in the fall.
The small, woody shrubs that are poison sumac are most common in the Eastern United States. Also known as Rhus vernix or Toxicondendron vernix, poison sumac differs in appearance from the three-leaf clusters of poison ivy and oak. It is feather-like in appearance, with two rows of leaves arranged on either side of a long stem, topped off by a long leaf at the tip. It can be distinguished from regular, non-poisonous sumac by its berries, which are green to white as opposed to the bright red berries of regular sumac.
According to the American Academy of Dermatology, an estimated 85 percent of the population is allergic to the urushiol oil found in poison ivy, oak, and sumac. Every year up to 50 million Americans develop a poison ivy, oak, or sumac rash. The chance of developing an allergic sensitivity to these poison plants decreases with age, and adults who have never been exposed to urushiol only have a 50 percent chance of developing contact dermatitis when exposed to poison ivy, oak, or sumac.
In addition, allergic sensitivity to poison plants tends to lessen with age. It is possible for children who are highly reactive to urushiol to grow into adults who are barely sensitive to poison ivy, oak, or sumac, regardless of how many times they have been exposed to the plant oil.
Causes and symptoms
While direct skin-to-plant contact with poison ivy, oak, or sumac is probably the most frequent cause of the rash, the irritants from the plants can also be passed on indirectly. Urushiol oil can be transmitted on clothing, pets, garden tools, shoes, or virtually anything that touches a plant.
Most children will not get a rash the very first time they are exposed to poison ivy, oak, or sumac, although this is when the sensitivity, or immune response, to urushiol develops. Not everyone acquires an allergic sensitivity to urushiol, but in those that do, the next time they are exposed to the plant and urushiol penetrates the skin, a rash is inevitable.
The first and most annoying symptom of a poisonous plant rash is severe itching. This may precede the rash or start at the same time as the rash appears. The rash, which is red and inflamed, usually begins to appear within two days after the initial exposure and is usually in a pattern of streaks or patches that approximates where the plant made contact with the skin. Blisters and/or red papules may form soon after the rash appears.
When to call the doctor
Mild cases of poison plant rash can usually be treated at home with over-the-counter creams and itch-relief measures, such as ice packs. A child who is not getting adequate relief from these treatments should see a doctor. Prescription cortisone cream or prednisone treatment may be necessary to relieve the itching.
Anyone who is experiencing symptoms of anaphylactic shock (such as difficulty breathing, dizziness , nausea , rash, swelling, itchy eyes, loss of consciousness) after exposure to poison ivy, oak, or sumac should be taken to the nearest hospital or emergency care facility for immediate treatment. Poison plant rashes that spread to the eyes and affect vision should also be treated by a doctor as soon as possible. If rash blisters are broken while scratching and begin to show signs of infection (for example, pain , swelling, puss, systemic fever ), a doctor should examine them as soon as possible in case antibiotics are necessary.
Poison plant rashes are diagnosed through an examination of the rash. A physician can distinguish poison ivy, oak, or sumac from other allergic contact dermatitis through a brief patient interview. If the contact with the plant was direct, the diagnosis may be obvious. If it was indirect (for example, from dog fur or garden tools), the doctor may need to rule out other allergies , especially if there were other new potential allergens in the child's environment (for example, a new pet, food, soap, or medication).
Treatments for the itching of poison ivy, oak, or sumac rashes range from calamine lotion and oatmeal baths to over-the-counter antihistamines and topical creams. Mild rashes may be relieved with a tub soak in baking soda solution, an oatmeal bath, or aluminum acetate (Domeboro solution). Calamine lotion and menthol ointments lessen the itching and dry out weeping blisters. Over-the-counter hydrocortisone creams and ointments and numbing sprays and lotions containing benzocaine and other anesthetic agents can relieve itching as well.
Benadryl and other oral antihistamines are also effective in soothing the discomfort and itch of poison plant rashes, but they can also cause drowsiness and are best used before bedtime.
In severe cases of poison plant rash, a prescription-strength cortisone cream or corticosteroid treatment (either oral or injections) may be required to relieve swelling and itching. These medications should be taken under a doctor's supervision according to the directions for use only for the period of time prescribed, as overuse of corticosteroid creams has the potential of interfering with a child's normal growth and development. Corticosteroid treatment may not be a preferred treatment in children with diabetes, as the drug has the potential of increasing blood glucose levels.
There are several lotions and creams on the market that remove urushiol oil from the skin and can prevent further spreading of the rash if oil remains, or even prevent the rash entirely if applied early enough following exposure. Rubbing (isopropyl) alcohol can also remove urushiol on both skin and household objects.
The sap of the jewelweed plant (Impatiens capensis ) is thought to be helpful in binding to and removing urushiol from skin. Either the plant itself (which grows wild in the Eastern United States, particularly in damp environments) can be rubbed on exposed skin, or a soap product made from Jewelweed (e.g., Burt's Bees Poison Ivy Soap) can be used to wash away urushiol. The plant must be used shortly after exposure to poison ivy, oak, or sumac to work.
A soak in tea tree oil (Melaleuca alternaifolia ) or the application of gel from the aloe vera plant can also be useful in alleviating itching and in drying the blisters of poison plant rash. Tea tree oil also has antiseptic properties and may be useful in warding off infection when poison plant rash blisters break. Jewelweed, tea tree oil, and aloe vera are not recognized by the U.S. Food and Drug Administration as treatments for poison plant rash.
The rash of poison ivy, oak, or sumac may last anywhere from a week to three weeks. In severe cases, it may linger up to a month. Usually there is no long-term effects or skin damage, but scratching that breaks the skin could potentially lead to permanent scarring. Infections can occur if blisters break and bacteria enters the open wound. Keeping the rash clean and any open blisters bandaged can lessen the chance of infection.
If urushiol enters the respiratory tract, which typically happens when the plant is burned and the smoke is breathed in, it can be life threatening. Anyone who encounters this type of exposure to poison ivy, oak, or sumac should seek emergency medical care immediately.
Children should be advised to stay out of areas where poison ivy, oak, or sumac is known to grow. When people are hiking or camping, exposed skin should be covered with long sleeves and pants. There are several topical skin creams on the market that contain bentoquatum, which forms a protective barrier designed to repel urushiol oil (e.g., Ivy Block, Stokoguard). These may be a useful preventative tool against poison plant rash as well.
If exposure does occur, washing with soap and cool water within the first 30 minutes of contact can sometimes prevent a rash. If soap is not available, rinse with water alone. A full body shower is best to eliminate all traces of the urushiol and prevent re-exposure from undetected oil remaining on other parts of the body. Again, water should be cool, as warm water will open pores and allow urushiol to penetrate the skin more quickly.
Other over-the-counter skin cleansers formulated to remove urushiol oil (e.g. Tecnu, IvyStat, IvyCleanse) can also stop or lessen the severity of a rash if they are applied early enough following exposure (i.e., before the urushiol begins penetrating the skin). These products can also be used to decontaminate garden tools and other items that have come in contact with the plant oil. Rubbing alcohol (isopropyl alcohol) is also helpful in decontaminating objects and skin.
Any clothing that has been exposed to poisonous plants should be handled carefully and laundered immediately. The same goes for shoes and garden gloves, which are common culprits of harboring urushiol oil. If possible, use latex or other disposable gloves to handle contaminated items and throw them away immediately afterwards.
Pet fur can also carry urushiol oil into the home. People should make sure outdoor pet areas are free of poisonous plants and never let a dog run unleashed in the woods or other areas with dense vegetation. Pets are typically not sensitive to urushiol, but a dog or cat that seems to be experiencing symptoms of poison plant rash following exposure should be taken to the veterinarian for assessment .
Eliminating known poison ivy, oak, or sumac growth in the yard or garden is also an important preventative step, but eradicating the weeds can be difficult. Glyphosate-based herbicides like Roundup and triclopyr-based herbicides like Ortho Brush-B-Gon will kill poison plants, but they can also take out any other surrounding foliage they come into contact with. If herbicides are used they should be applied carefully and may have to be rubbed directly on to the leaves and stems to avoid damaging other plantings.
Another option for eliminating poison plants is to pull them by hand. Proper protection of all exposed skin is important to prevent a reaction. The entire plant, including the root system, must be pulled. As an alternative, landscaping fabric or another barrier can be placed over poison ivy, oak, or sumac to kill the plants and prevent future growth. Dead plants still contain urushiol and must be handled carefully during removal. All plants should be disposed of according to local waste regulations. Never compost or burn poison plants because of the potential of spreading the oil through the garden or air. Mowing over the vines or plants can also send urushiol into the air and has the potential to cause a serious allergic reaction.
The itching and discomfort of poison ivy, oak, and sumac rashes can disrupt sleep , make a child irritable and anxious, and pose a major distraction to schoolwork and other tasks that require concentration.
Soothing the itching is the best way to help a child get through the misery of a poisonous plant rash. Covering the affected areas with bandages may be useful in curtailing scratching and preventing potential scarring. A child's fingernails should be kept clean and trimmed short to lessen the chance of bursting and infecting blisters if scratching does occur.
Corticosteroids —A group of hormones produced naturally by the adrenal gland or manufactured synthetically. They are often used to treat inflammation. Examples include cortisone and prednisone.
Papule —A solid, raised bump on the skin.
Urushiol —The oil from poison ivy, oak, and sumac that causes severe itching, blistering, and rash.
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Poison ivy (Toxicodendron radicans ) is a nuisance plant that grows throughout the continental United States. It grows in almost any type of soil, in both the shade and the sun. While it is most commonly found as a trailing vine, it can also form an upright shrub, and can climb trees, boulders, or walls to heights of 15 meters (50 feet). Its seeds are an important winter food for many types of birds.
Poison ivy's oil causes an itchy, blistering rash in most people who come in contact with it. All parts of the plant contain the oil, although the leaves are the most easily bruised and are therefore the most likely to cause the rash. The oil is sticky and will cling to (and be spread on) skin, clothing, tools, and animal fur. It is also spread in smoke when the plant is burned. In fact, irritation from poison ivy smoke is a major cause of temporary disability in forest fire fighters.
The active ingredient of the oil is urushiol (you-ROOSH-ee-ol). Urushiol is absorbed quickly into the skin. The itching and blistering that results is not due to direct damage done by urushiol, but by the allergic reaction mounted by the immune system. Relatively few people are actually immune to the effects of urushiol, although sensitivity varies and can change over time. Washing the oil off immediately after contact can help reduce the likelihood of developing a rash. In recent years, a clay-based lotion has been shown to help prevent the rash by binding to the urushiol before it can penetrate the skin.
Rashes last approximately two weeks. Some people find relief from the itching and blistering by applying calamine lotion or the mucilaginous sap of jewelweed (Impatiens capensis ). Hot water can provoke a short-lived, intense irritation followed by a longer period of relief. Prescription corticosteroid creams are used for severe cases.
Recognizing the plant is the best way to avoid it. The three leaflets of poison ivy are from 3 to 15 centimeters long, smooth to slightly indented at the edges, shiny and reddish in spring but becoming a glossy to dull green in summer. "Leaflets three, let it be; berries white, poisonous sight" is a handy way to remember the characteristic appearance of poison ivy.
Poison oak, which grows in California, Oregon, and Washington, has a somewhat similar appearance, while poison sumac grows as a shrub and has a compound leaf and drooping clusters of green berries (unlike other sumacs, which have upright clusters or red berries). All three plants are members of the family Anacardiaceae, many of whose members—including mango and cashew—also contain skin irritants in some plant parts.
see also Defenses, Chemical; Lipids; Poisonous Plants.
Darlington, Joan R. Is It Poison Ivy: Field Guide to Poison Ivy, Oak, Sumac and Their Lookalikes, 2nd ed. Durham, NH: Oyster River Press, 1999.
poi·son i·vy • n. a North American climbing plant (Rhus radicans) of the cashew family that secretes an irritant oil from its leaves, which can cause dermatitis.