Can You Immunize Yourself Against Poison Ivy?

I loved your interview with Gideon Lack. I told my dad about the novel theories of allergies, and it jogged his memory from when someone told him (he thinks while on the Appalachian Trail) that the best way to immunize yourself from poison ivy is to eat it. Is there any evidence for this, and should I be feeding my child poison ivy?

—KT

Thanks for listening! As you note, the ideas we talk about there do seem related to your dad’s crazy idea.

Is it true?

I began this investigation with a delightful article from 1931 about poison ivy. I learned a lot (it’s actually not an ivy, that’s just the name Captain John Smith gave it; few if any people are immune; etc.), but I did not learn the answer to your question. This author notes that it is a commonly discussed possibility, and he thinks it has some possible support given that it was a long-standing tradition among some Native American tribes in the Pacific Northwest. However, there is no compelling data.

Things haven’t changed too much since 1931! A 2019 summary has only slightly more evidence to bring to bear. A number of studies have tried using poison ivy or an oil extract to generate desensitization to skin exposure. For the most part, these are not studies of people eating poison ivy (which may well give you a contact rash in your mouth, and you probably should not do) but people taking pills with poison ivy extract. And the studies are not large. They are like this one, which rely on a small number of case reports and experimental doctors’ treatment.

These studies all claim to show some promise, enough that I’d be interested in seeing what you’d get with a large randomized controlled trial. But I do not read the evidence as close to strong enough that you’d want to dose your child. For now, better to teach them what poison ivy looks like and that they should not touch it.