The three most common causes of allergic skin reactions in the United States are poison ivy, poison sumac, and poison oak. These plants are all a type of weed. Poison ivy grows in the east. Poison oak grows in the west. Both poison sumac and poison ivy grow in the south. There is no generic form of poison oak or poison ivy. The plants adapt to the environment and the leaflets may vary from groups of three, to groups of five, seven, or even nine.

Contact with these plants causes a rash called allergic contact dermatitis. These plants release a sap that has a poisonous oil. The poisonous oil spreads to objects that contact the plant. It penetrates skin quickly and causes a rash within 12 to 48 hours. The first reaction produces a rash showing redness and swelling. These symptoms are followed by blisters and severe itching. In a few days the blisters become crusted and begin to scale. The dermatitis usually heals within ten days.

Begin treatment within 5-10 minutes, if possible, by washing all exposed areas in cool running water and soap. Doing so will keep the poisonous oil from spreading to other parts of the body. All items worn or carried when exposed to the poisonous plants should be washed with soap and water when a stream, lake, or garden hose is reached. Water deactivates and neutralizes the poisonous oil and keeps it from spreading. Cool compresses and cool showers will ease the itching. Baking soda baths will help dry the lesions. Over-the-counter preparations, like calamine lotion, will relieve mild rashes. Talk with a pharmacist or health care provider if itching is severe or rash becomes infected.

The best prevention is to recognize these plants and stay away from them. The old saying, "leaves of three, let them be", is usually reliable, but beware. The appearance of these plants can vary considerably. Poison ivy grows as a low shrub or vine. Poison oak is a low shrub or small tree and has groups of yellow berries. Poison sumac is a tall shrub with cream-colored berries.

The poisonous oil from these plants can remain active for months. So be sure to wash all camping, fishing or hunting gear, and pets that may be carrying it, too.

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