What are poison ivy, oak, and sumac?

Poison ivy, poison oak, and poison sumac are plants that can cause a skin rash called allergic contact dermatitis when they touch your skin. The red, uncomfortable, and itchy rash often shows up in lines or streaks and is marked by fluid-filled bumps ( blisters) or large raised areas ( hives). It is the most common skin problem caused by contact with plants (plant dermatitis).

See a picture of poison ivy, oak, and sumac leaves .

What causes a poison ivy, oak, or sumac rash?

The rash is caused by contact with an oil (urushiol) found in poison ivy, oak, or sumac. The oil is present in all parts of the plants, including the leaves, stems, flowers, berries, and roots. Urushiol is an allergen, so the rash is actually an allergic reaction to the oil in these plants. Indirect contact with urushiol can also cause the rash. This may happen when you touch clothing, pet fur, sporting gear, gardening tools, or other objects that have come in contact with one of these plants. But urushiol does not cause a rash on everyone who gets it on his or her skin.

What are the symptoms of the rash?

The usual symptoms of the rash are:

• Itchy skin where the plant touched your skin.
• Red streaks or general redness where the plant brushed against the skin.
• Small bumps or larger raised areas ( hives).
• Blisters filled with fluid that may leak out.

The rash usually appears 8 to 48 hours after your contact with the urushiol. But it can occur from 5 hours to 15 days after touching the plant. ¹ The rash usually takes more than a week to show up the first time you get urushiol on your skin. But the rash develops much more quickly (within 1 to 2 days) after later contacts. The rash will continue to develop in new areas over several days but only on the parts of your skin that had contact with the urushiol or those parts where the urushiol was spread by touching.

The rash is not contagious. You cannot catch or spread a rash after it appears, even if you touch it or the blister fluid, because the urushiol will already be absorbed or washed off the skin. The rash may seem to be spreading, but either it is still developing from earlier contact or you have touched something that still has urushiol on it.

The more urushiol you come in contact with, the more severe your skin reaction. Severe reactions to smaller amounts of urushiol also may develop in people who are highly sensitive to urushiol. Serious symptoms may include:

• Swelling of the face, mouth, neck, genitals, or eyelids (which may prevent the eyes from opening).
• Widespread, large blisters that ooze large amounts of fluid.