Exams and Tests

A rash (allergic contact dermatitis) from poison ivy, oak, or sumac plants usually is diagnosed through a physical exam and questions about your outdoor activities. Your doctor will examine the rash to decide which kind of plant caused it and ask about:

• The length of time between possible exposure and development of the rash.
• The length of time you were out in the sun.
• What you were doing when the exposure may have occurred (hiking, for example).
• Other rashes you have had.
• Your job and your hobbies.

Diagnosis is harder when there are no clues that you have been in contact with the plant. Sometimes indirect contact with the plant oil (urushiol) causes the rash. Urushiol that is on clothing or other objects may spread to your skin months after initial contact. If a bacterial infection is suspected, your doctor may take a sample of blister fluid for a culture.

If your primary care doctor is not sure of the cause, you may need to see a dermatologist for a direct patch skin test. In this test, small amounts of allergens are placed on the skin and covered with a bandage for several days. The patch is then removed and the skin is examined for reactions.

Treatment Overview

The rash (allergic contact dermatitis) from poison ivy, oak, or sumac generally is mild and can be treated at home. Home treatment for the rash usually helps relieve symptoms but does not speed up healing of the rash.

• If you know you had contact with one of these plants, immediately wash areas of the skin that may have touched the plant. Sometimes the rash can be completely avoided by washing the affected areas with plenty of water within 10 or 15 minutes of contact. You could also try using a product (such as Tecnu or Zanfel) that is designed to remove the oil from your skin.
• To relieve itching and help dry blisters, apply wet compresses or soak the area in cool water. Antihistamine pills or calamine lotion may help relieve symptoms.
• If you have a moderate to severe rash, you may need to see your doctor. He or she may prescribe corticosteroid pills. These medicines may help improve or clear up the rash more quickly. Prescription corticosteroid creams, ointments, gels, or shots may also be used.

A frequent complication of the rash is infection. If this occurs, your doctor will probably prescribe an antibiotic cream that you spread on the affected skin if the infection is small. Otherwise, you may need antibiotic pills or a shot. To prevent infection, try not to scratch the rash. Cut your fingernails short to minimize the possibility of opening the skin and spreading bacteria.

Regardless of what type of treatment is used after a rash develops, the length of time it lasts will vary from person to person.