Can You Build Immunity to Poison Ivy by Eating It?

I have a friend who is a city arborist. He knows a bit about plants as well as trees. He told me that it was possible to build up a relative immunity to poison ivy by ingesting the leaves of the plant in small doses over time. Is this true? —Josh, Knoxville, TN

When you’ve suffered an exposure to poison ivy, it’s not surprising that you’d be eager to avoid a repeat. The angry red rash, the burning and itching that can last for days—who wouldn’t be desperate to find a way to prevent it from happening again?

Eating poison ivy isn’t the solution you’re looking for. Whether you got the idea from a well-meaning but misguided friend or from watching the poison-resistant Dread Pirate Roberts best Vizzini in a battle of wits in The Princess Bride (classic), the fact is that you can’t develop an immunity to poison ivy by consuming it.

To explain why, we have to talk a little bit about why poison ivy hurts so bad. The substance responsible for your agony is urushiol, an oily resin found in poison ivy as well as some other species like poison oak, poison sumac, and Toxicodendron vernicifluum, the Chinese lacquer tree. Brush up against an urushiol-containing plant, and you’re potentially in for a bad week or so of swelling, burning, and blisters.

But despite the name, urushiol isn’t actually poisonous—that’s why dogs and and other mammals that are relatively similar to humans don’t get symptoms from exposure to it. Instead, those nasty symptoms are part of an allergic response, like some people experience from bee stings or dust. About 15 percent of people aren’t allergic to urushiol, meaning that they can touch poison ivy to their hearts’ content and walk away none the worse for wear.

Unfortunately for the rest of us, eating poison ivy won’t decrease that allergic response. In fact, it’s likely to make it worse: Repeated exposure to urushiol can sensitize you, leading to progressively worse reactions. And getting it inside your mouth? Shiver.

Instead of chomping down on a big bowl of poison ivy salad, opt for prevention. Wear long sleeves and pants if you’re planning on going off-trail in an area where poison ivy is common. If you realize you’ve been exposed, wash the affected area with soap and water as soon as possible to prevent the urushiol from binding to your skin. A specialized poison ivy wash like Tecnu may help provide an additional punch.