How to Treat Poison Ivy and Poison Oak Allergic Rashes

Many of us have come into contact with poison ivy, poison oak or poison sumac at one time or another. Maybe this exposure came as a result of hiking or camping, or from trying to get the backyard weeds under control. Of course, there's a chance that we might not remember when we actually came into contact with these plants, but we certainly can’t forget the itchy rash that came as the result.

Plants from the Toxicodendron genus are the most common cause of allergic contact dermatitis and include poison ivy, poison oak, and poison sumac. Coming into contact with these plants results in the deposition of oils from the leaves onto the skin, which can cause an itchy rash consisting of a linear, or streak-like group of blisters or bumps.

The chemicals released from the plants, called urushiols, cause the itchy rash through an immune reaction different from an allergic reaction (meaning that there are no allergic antibodies involved). Most people develop contact dermatitis as a result of skin contact with urushiols, but not everyone.

Poison oak

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After exposure to Toxicodendron plants, an itchy, blistering skin rash will occur within a day or so at the site of contact. Since the part of the immune system that reacts to the urushiol has a memory, it is common for any other areas of the body recently exposed to Toxicodendron plants to also develop a rash.

Urushiol can be carried on the fur of animals, garden tools, sports equipment, and clothing, among other things. The smoke from burning leaves of these plants can also carry urushiol, resulting in inflammation in the lungs if inhaled.

Surprise Concerns: Mangoes and Cashews

Mangoes and cashews are in the same biological family as the Toxicodendron genus, and they have the ability to cause rashes similar to those from poison ivy and poison oak. Contact with the skin from mangoes or with the oil from cashews can result in a rash around the mouth. These symptoms may include redness, itching, and flaking on the areas of skin that these foods touched.

Diagnosis of Poison Ivy and Poison Oak Rashes

Patch testing is not necessary to diagnose contact dermatitis from poison ivy or poison oak. Most people would have a positive test, and the diagnosis is best made when a person has a rash consistent with poison ivy or poison oak, along with a history of recent exposure to Toxicodendron plants.

Treating Rashes

Preventing contact with Toxicodendron plants is the best way to prevent getting the rash. If you are planning on being in an area where contact with poison ivy or oak is likely, wearing pants, long-sleeved shirts, shoes, and socks can prevent the plant oils from getting onto your skin.

Applying Ivy Block (an over-the-counter lotion that absorbs urushiol) to exposed skin, in much the same way that sunscreen is applied, may prevent the rash from occurring if used before contact with these plants.

If contact with poison oak or ivy does occur, washing the area thoroughly with soap and water immediately after contact may prevent or minimize the amount of rash that occurs. Any clothing that comes into contact with Toxicodendron plants should be removed and laundered before wearing it again.

If a contact dermatitis rash does occur after exposure to Toxicodendron plants, using prescription topical steroids to reduce the rash and itching can help. If the rash is severe or over large areas of the body, oral or injected steroids may be necessary to treat the symptoms. Because the rash is not caused by the release of histamine, antihistamine medications (like Benadryl) are not useful for treatment.

Learn more about the different anti-itch creams that are available without a prescription.

Is There a Cure for Poison Ivy and Poison Oak Reactions?

While the rashes caused by Toxicodendron plants are treatable, there is no way to prevent these reactions from occurring aside from avoiding contact with these plants, since these rashes are not caused by allergic antibodies like true allergic reactions. Therefore, allergy shots do not work to prevent poison ivy or oak reactions, and there is no way to cure these types of reactions with pills or injections.

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  2. Scientific American. What do cashews, mangoes and poison ivy have in common?

  3. U.S. National Library of Medicine, MedlinePlus. Bentoquatam topical.