Posion Ivy

June 1, 2019
By Jessica Duke, MD

What do these patients have in common?


  • A 4-year-old with lines of red bumps and blisters over his legs after playing in the woods behind his house.
  • A 46-year-old female with swelling and irritation around her bottom after wiping herself with dead leaves while hiking yesterday.
  • A 22-year-old male with difficulty breathing after a bonfire this evening.


If you guessed an allergic reaction to urushiol-containing plants, such as poison ivy, you’re right!


Poison ivy or Toxicodendron radicans is a member of the Anacardiaceae plant family that also includes poison oak, sumac, cashew, pistachio, and mango. These plants produce urushiol, a compound that can cause an allergic reaction known as urushiol-induced contact dermatitis. This reaction occurs when urushiol binds to the skin after direct contact with the broken leaves or stems of the plant, indirect contact by touching something that has urushiol on it (like a pet or garden tool), or through airborne exposure to burning plants. The body’s immune system then attacks the skin containing the urushiol. For people who have never been exposed to urushiol, it may take up to 3 weeks for the symptoms to first appear. However, on future exposures, symptoms will appear within days. This is known as delayed type or type IV hypersensitivity. Symptoms include more mild reactions such as red itchy rashes, oozing blisters, and swelling to life threatening reactions such as pulmonary edema and anaphylaxis.


How can you prevent exposure to poison ivy and what can you do if you do become exposed?


Prevention is the best form of protection against poison ivy. The most important part of prevention is to know how to identify these plants so you can avoid them. Poison ivy is found throughout the United States east of the Rocky Mountains. It grows as a bush or vine and is easily identified by its compound leaves composed of three almond-shaped leaflets that alternate on the stem or vine. Other identifying characteristics include a center leaf that is slightly larger than the two side leaves, a smooth and somewhat shiny leaf surface, smooth or notched but not serrated leaf edges, and hairy vines without thorns. Even if you do know how to identify the plant, you may want to consider wearing protective clothing, including long pants, long-sleeved shirts, and gloves if you know will be in an area with poison ivy. After being in an area with poison ivy, wash all clothing, shoes, tools, and pets that may have been exposed, as the urushiol can remain active for several years. If your skin was exposed to poison ivy, cleanse the area immediately with soap and water to remove the urushiol before it has a chance to bind. Furthermore, if you know you are allergic to poison ivy, be sure to wash your hands right after eating cashews, pistachios, and mangos, especially if handling the shells or skin. Lastly, do not burn poison ivy as the smoke can cause a potentially deadly inhalation reaction.


As mentioned above, the first thing to do after exposure to poison ivy is to immediately cleanse the area with soap and water to prevent the urushiol from binding to the skin. If signs or symptoms of urushiol-induced contact dermatitis do appear, try cool compresses, oatmeal baths, antihistamines, and steroid creams to help relieve itching. In more severe cases, patients may require a 14 to 21-day course of an oral steroid taper to attenuate the immune response or antibiotics if a secondary bacterial infection occurs. Inhalation reactions are potentially fatal and may require hospitalization.