]Poison ivy, poison oak and poison sumac are the most common cause of allergic reactions in the United States. These plants grow almost everywhere in the United States, except Hawaii, Alaska and some desert areas in the western U.S. Poison ivy usually grows east of the Rocky Mountains and in Canada. Poison oak grows in the western United States, Canada, Mexico (western poison oak) and in the southeastern states (eastern poison oak). Poison sumac grows in the eastern states and southern Canada.

A poison plant rash is an allergic contact dermatitis caused by contact with oil called urushiol. Urushiol is found in the sap of these pointy plants. It is colorless or pale yellow oil that oozes from any cut or crushed part of the plant, including the roots, stems and leaves. After exposure to air, urushiol turns brownish-black. Damaged leaves look like they have spots of black enamel paint making it easier to recognize and identify the plant. Contact with urushiol can occur in three ways: direct contact (touching the sap of the toxic plant); indirect contact (touching something on which urushiol is present); and airborne contact (burning poison plants and putting urushiol particles into the air).

It is important to recognize these poison plants: 

Poison Ivy: each leaf has three leaflets; can be vines or low shrubs
Poison Sumac: has a row of paired leaves, and the middle or end leaf is on a longer stalk than the other leaves, which differs from most other three-leaf look-alikes; is a tall shrub or small tree.
Poison Oak: each leaf has three leaflets, much like poison ivy. These plants take various forms depending on in which region they grow; can be a low or high shrub.

If you think you’ve come in contact with one of these poison plants, see your dermatologist. He or she will be able to determine which plant and the proper treatment for you.

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