Urushiol is found in all parts of these plants, including the leaves, stems, and roots, and is even present after the plant has died. Urushiol is absorbed quickly into the skin. It can also be inhaled if the poison plants are burned. The smoke may expose not only the skin to the chemical but also the nasal passages, throat, and lungs. Inhaled urushiol can cause a very serious allergic reaction.
The rash that results from the poison plants is a form of allergic contact dermatitis. (Dermatitis is swelling and irritation of the skin.) Skin is not automatically sensitive to urushiol. Sensitivity builds up after the skin is exposed to the substance. When initially exposed to urushiol, the skin alerts the immune system of the presence of the irritating chemical. However, it's common for no visible reaction will occur the first time a person comes in contact with a poison plant. The immune system then prepares a defensive reaction for the next time the skin encounters the substance. This sensitizes the skin so that new contact with urushiol causes an allergic reaction.
Poison ivy, poison oak, and poison sumac can be found in most areas of the U.S., except Alaska, Hawaii, and the deserts of the Southwest. In some areas of the country (East, Midwest, and South), poison ivy grows as a vine. In the northern and western U.S., and around the Great Lakes, it grows as a shrub. Each poison ivy leaf has three leaflets.
Poison oak closely resembles poison ivy, although it is usually more shrub-like, and its leaves are shaped somewhat like oak leaves. The undersides of the leaves are always a much lighter green than the surface and are covered with hair. Poison oak is more common in the western U.S.
Poison sumac grows as a woody shrub, with each stem containing 7 to 13 leaves arranged in pairs. Poison sumac can be distinguished from harmless sumac by its drooping clusters of green berries. Harmless sumac has red, upright berry clusters. Poison sumac is more common in wet, swampy areas.
