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Poison Ivy, Poison Oak, Poison Sumac

The poison ivy plant is known as Toxicodendron radicans in the eastern US and T. rydbergii in the midwestern US. It is also called Rhus toxicodendron . Western poison oak is known as Toxicodendron diversilobum .

These plants can cause a skin reaction. No reaction usually occurs the first time the skin is exposed to the plant. Subsequent contact with the plant or plant resin, however, may result in an allergic skin reaction which usually appears 7-14 days after contact. Subsequent contact results in a more rapid reaction, usually within 2-5 days post-contact. The severity of the reaction is related to the amount of plant material which comes in contact with the skin, as well as to the degree of allergic sensitivity of the individual. The allergen (irritant from the plant) is often transferred from the hands or clothing to other parts of the body.

The poison ivy plant and its relatives are common throughout the United States. Poison ivy leaves are coated with a mixture of chemicals called urushiol. When people get urushiol on their skin, it causes allergic contact dermatitis . The body's immune system treats urushiol as foreign and attacks the complex of urushiol-derivatives with skin proteins. The irony is that urushiol, in the absence of the immune attack, would be harmless.

Poison ivy can affect two out of three Americans and of these, 15 percent may have severe allergic reactions which require medical treatment. In 1994, more than nine million Americans sought remedies for the irritation, caused by poison ivy, oak and sumac (cf. Toxicodendron Dermatitis ).

 

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  http://www.hon.ch/Library/Theme/Allergy/Glossary/poison.html Last modified: Fri Jun 28 2002