Plants from the Toxicodendron genus are the most common cause of allergic contact dermatitis and include poison ivy, poison oak, and poison sumac. Touching 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 that is different from an allergic reaction—meaning that there are no allergic antibodies involved. Since the reaction is not exactly the same as an allergic reaction—treatment and prevention aren’t the same as treatment and prevention of skin allergies.
Poison Oak and Poison Ivy Reactions
Most people develop contact dermatitis as a result of skin contact with urushiols, but not everyone has this reaction.
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, future exposures to Toxicodendron can result in quicker onset and/or more severe rashes.
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 cashew nutshells can also result in a rash. 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
The diagnosis of poison ivy or poison oak rash is made when a person has a rash consistent with poison ivy or poison oak, along with a history of recent exposure to Toxicodendron plants.
Patch testing is not necessary to diagnose contact dermatitis from poison ivy or poison oak and most people would have a positive test.
Preventing and 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. Ivy Block, an over-the-counter lotion that prevents urushiol from coming into contact with the skin, can be applied to areas of the skin at risk for exposure in much the same way that sunscreen is applied. It may prevent the rash from occurring if used before contact with these plants.
Treatment
If a contact dermatitis rash occurs after exposure to Toxicodendron plants, you can consider using anti-itch creams that are available without a prescription. Because the rash is not caused by the release of histamine, antihistamine medications (like Benadryl) are not useful for treatment.
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.
Is There a Cure for Poison Ivy and Poison Oak Reactions?
The rashes caused by Toxicodendron plants are treatable. The only way to prevent the reactions from occurring is by avoiding contact with these plants. Since these rashes are not caused by allergic antibodies like true allergic reactions, allergy shots do not work to prevent poison ivy or oak reactions.
