Poison ivy, poison sumac, and poison oak are 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.
Poison ivy, poison oak, and poison sumac grow almost everywhere in the United States except Hawaii, Alaska and some desert areas of Nevada. Poison ivy usually grows east of the Rocky Mountains and in Canada. Poison oak grows in the Western United States, Canada and Mexico (western poison oak), and in the southeastern states (eastern poison oaks). Poison sumac grows in the eastern states and Southern Canada.