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Poison Ivy

By

Thomas M. Ruenger

, MD, PhD, Georg-August University of Göttingen, Germany

Last full review/revision Apr 2021| Content last modified Apr 2021
Click here for the Professional Version
Topic Resources

Poison ivy is an allergic contact dermatitis that causes a very itchy rash caused by exposure to the oil urushiol, which coats the leaves of poison ivy plants.

  • An itchy, red rash and multiple blisters develop in the area where the plant came in contact with the skin.

  • Doctors base the diagnosis on the person's exposure and the appearance of the rash.

  • People should learn how to recognize the plant and avoid it.

  • Treatment includes applying corticosteroids and using other measures to relieve symptoms.

About 50 to 70% of people are sensitive to the plant oil urushiol contained in poison ivy, poison oak, and poison sumac. Similar oils are also present in the shells of cashew nuts; the leaves, sap, and fruit skin of the mango; and Japanese lacquer. Once a person has been sensitized by contact with these oils, subsequent exposure causes a rash (allergic contact dermatitis).

The oils are quickly absorbed into the skin and stick to skin tightly, to clothing, to items such as outdoor tools or equipment, and to pet fur for long periods of time and can still cause the rash. Smoke from burning plants also contains the oil and may cause a reaction in certain people.

Symptoms

Symptoms of poison ivy dermatitis begin 8 to 48 hours after contact and consist of intense itching, a red and sometimes swollen rash, and multiple blisters, which may be tiny or very large. Typically, the blisters occur in a straight line in the area where the plant brushed along the skin. The rash may appear at different times in different locations because of repeat contact with contaminated clothing and other objects or because some parts of the skin are more sensitive than others. The blister fluid itself is not contagious. The itching and rash can take several weeks to go away after the last exposure.

Diagnosis

  • A doctor's evaluation

Doctors base the diagnosis of poison ivy dermatitis on the characteristic rash and the person's exposure to urushiol.

Prevention

Recognizing and avoiding the plants is the best prevention. Poison ivy plants (Toxicodendron radicans) grow throughout the United States except Alaska, Hawaii, and parts of the West Coast. The plant leaves are arranged in groups of three ("leaves of three, let it be") and are shiny green (or red in the fall). The center leaf has a longer stem than the other two. Poison ivy can grow as a hairy, ropelike vine or as a free-standing shrub. The plants may have green or yellow flowers and white to yellow berries.

Before exposure, if people are going to be in areas where the plants grow, they should wear long sleeves, long pants, boots, and gloves and avoid the plants if possible. A number of commercial barrier creams and lotions can be applied before exposure to minimize, but not completely prevent, absorption of oil by the skin. The oil can soak through latex rubber gloves. People should not try to desensitize themselves by taking various shots or pills or by eating poison ivy leaves because these measures do not work.

After exposure, people should immediately wash their skin with soap and water to prevent absorption of the oil. Stronger solvents, such as acetone, alcohol, and various commercial products, are probably no more effective than soap and water. Exposed clothing should be washed separately in hot water with detergent.

Treatment

  • Corticosteroids applied to the skin or taken by mouth

  • Measures to relieve symptoms

The most effective treatment is with corticosteroids. Small areas of rash are treated with strong corticosteroids applied to the skin, such as triamcinolone, clobetasol, or diflorasone. However, if the face and genitals are affected, strong corticosteroids should not be used or should be used only for short periods of time because they can otherwise damage this delicate skin. People with large areas of rash or significant facial swelling are given corticosteroids taken by mouth.

Cool compresses wet with water or aluminum acetate may be used on large blistered areas. Antihistamines given by mouth may help with itching. Calamine lotion or lotions with cooling agents, such a menthol and camphor, can help to control itching.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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