Poison Ivy is a plant (more specifically, a woody vine or shrub) that has a wide distribution. It may be found coast to coast from southern Canada to Mexico. It is also found from the West Indies and China. It is a member of the Anacardiaceae, or cashew family. Most members of this family have a tropical or sub-tropical distribution. In North America, it is represented by the poison ivy, poison oak, poison sumac and the Florida Poison Tree.
Poison Ivy is dangerous because it contains a chemical that can cause skin to develop a red, itchy rash and even erupt in blisters. Urushiol is the active ingredient in poison ivy that causes this rash and irritation. It is present in all parts of the plant, but particularly in the sap. People vary in their sensitivity to urushiol; some have no problem with it and others experience severe allergic reactions. This can also vary over the life of a person. One may be unaffected as a child and become sensitized with repeated exposures.
The irritation that poison ivy causes usually starts as itching and small blisters within a few hours after exposure. Depending on how strong the exposure was and/or how sensitive the person is, that may be the only effect. However, it may develop into an inflamed, swollen rash with open oozing sores that persists for up to two weeks. Severe cases may require a visit to the doctor. Urushiol is absorbed into the skin within three minutes of exposure.