A patient recently came in to our dermatology clinic with a rash and a story similar to so many others. He had been out camping with friends a few days earlier and helped carry some logs to stoke the fire. Little did he know he was going to pay for lending a helping hand. A couple days later, red patches appeared on his forearms and chest, which soon began to itch miserably and form water blisters.
If you have ever spent any time outdoors – in the woods, working in the yard, even at the edges of a playground – maybe you’ve experienced something similar after encountering poison ivy. It’s not easy to forget.
Encounters with a botanical irritant
Poison ivy is found everywhere in the continental U.S., mostly in Eastern and Midwestern states. Unfortunately for us humans, it is a hardy plant that can grow under many different conditions. Its favorite places are in wooded areas, gardens and roadsides with partial shade or full sunlight.
And despite being a nuisance to people, poison ivy is an important member of the ecosystem. Its leaves, stems and berries are food for animals, and its vines can be shelter for small animals like toads and mice, even helping them climb trees. Climate change is turning out to benefit poison ivy, allowing for larger and more irritating plants.
You can usually spot poison ivy by its infamous three dull or glossy green leaves coming off a red stem. Sometimes there are flowers or fruits coming off the end of a branch.
Despite its name, poison ivy is not poisonous. It carries an oily sap on its leaves and stems called urushiol, which is irritating to most people’s skin. In fact, 85% to 90% of people are allergic to poison ivy’s urushiol to some degree, while the rest lack sensitivity to this oil. You can occasionally see the urushiol oil as black spots on poison ivy leaves. Urushiol is what gives poison oak and poison sumac their evil power, too.
Touching poison ivy...
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