A: Poison oak, in the Western and Southeastern United States and poison ivy, in the Eastern United States, are common wild plants that cause allergic skin rashes. Poison oak and poison ivy can grow as bushes and vines and both have a characteristic shiny green or reddish three-leaf appearance. The skin rash is caused by contact with the oils on the leaves, stems or other parts of the plant. In people who are allergic, the rash usually takes one to two days to develop, but it can develop as quickly as 30 minutes after contact or as long as two weeks afterward.

The rash can appear as redness and swelling with raised bumps or blisters that may leak a watery fluid, which later becomes crusty. These bumps and blisters are often found in a line, corresponding to how the leaf brushed against the skin. The rash is usually worse around the fifth day and usually resolves within two weeks.

Although it might seem like the poison oak is spreading by the watery fluid in the blisters, it’s not contagious to other parts of the body or other people. The rash develops only after contact with the oil from the leaves or contact with oils left under the fingernails or on clothes or pets that touched the leaves. When the rash comes out on certain parts of the body first and other parts later, it’s usually because some parts were more exposed than others.

However, it’s important to make sure that your daughter is not continuing to be exposed to the oil by scratching herself with unwashed hands, by touching the clothes or shoes she wore that day or hugging the dog. Give her a bath or shower and have her wash her skin and hands well with soap. Also, wash her clothes and shoes, being careful not to exposure yourself to the oils. And, give the dog a bath.

If your daughter is bothered by itchiness you can put an anti-itch lotion such as calamine on the rash. Sometimes cool compresses or an oatmeal bath can help. If she’s scratching more at night, consider giving her an over-the-counter anti-histamine medicine to reduce the itchiness. Contact your doctor if the rash is on her eyes, lips or genitals, if it covers over a third of her body, if it isn’t getting better within a week or two or if it appears to be getting worse. Sometimes an oral steroid is needed to control the rash or an antibiotic if the rash has become infected.

To prevent poison oak in the future, show your daughter pictures of the leaves and tell her to stay away from them: “Leaves of three, let them be.” When you take her and the dog to the park, wear long pants and long-sleeve shirts and stay in open areas and on groomed trails. After returning home from the park, have your daughter take a bath or shower, throw her clothes into the laundry and give the dog a bath.

For more information, visit the American Academy of Dermatology website aad.org/public/Publications/pamphlets/Poison_IvyOakSumac