Allergies Contact Dermatitis How to Treat Poison Ivy and Poison Oak Allergic Rashes By Daniel More, MD Daniel More, MD, is a board-certified allergist and clinical immunologist with a background in internal medicine. Learn about our editorial process Daniel More, MD Medically reviewed by Medically reviewed by Casey Gallagher, MD on July 21, 2020 Casey Gallagher, MD, is board-certified in dermatology and works as a practicing dermatologist and clinical professor. Learn about our Medical Review Board Casey Gallagher, MD on July 21, 2020 Print 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 family 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. 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. Ed Reschke / Getty Images Surprise Concerns: Mangoes and Cashews Mangoes and cashews belong to the Toxicodendron family, 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. Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Beltrani VS, Bernstein IL, Cohen DE, Fonacier L. Contact Dermatitis: A Practice Parameter. Ann Allergy Asthma Immunol. 2006;97: S1-38.