Dermatology Facts—Poison Oak

Poison oak, poison ivy and poison sumac are the most common cause of allergic reactions in the United States. Each year 10 to 50 million Americans develop an allergic rash after contact with these plants.

Why do these plants cause itch?

A chemical called urushiol causes the rash, blisters and itch. It is found in the sap of poison oak, poison ivy and poison sumac plants. Urushiol (pronounced oo-roo-shee-ohl) is released from any damaged part of these fragile plants. Even the tiniest hole in the plant can release the irritating sap which looks brownish-black when exposed to air.