Allergens: Poison Ivy

What is poison ivy?
There are three native American plants that collectively may be called poison ivy: poison ivy, poison oak, and poison sumac. These plants cause an allergic reaction in nearly 85 percent of the population.

What causes the allergic reaction?
The resin in the plants contains an oily substance called urushiol. Urushiol is easily transferred from the plants to other objects, including tools and animals. This chemical can remain active for a year or longer.

What is the allergic reaction to poison ivy?
The reaction is usually contact dermatitis, which may occur several hours, days, or even weeks after exposure. The dermatitis is characterized by a rash followed by bumps and blisters that itch. Sometimes swelling occurs in the area of contact. Eventually, the blisters break, ooze, then crust over.