Don't Touch! A Scientist's Advice For Spotting Poison Ivy Before It Ruins Your Summer

WPLN | By Blake Farmer

Published June 8, 2018 at 8:36 AM MST

Microbiologist John Jelesko has learned not to take any chances when he touches poison ivy.

It was a close encounter in 2012 that made microbiologist John Jelesko take an interest in poison ivy.

The Virginia Tech professor was cutting up a downed tree with an electric chainsaw. What he didn't realize was that his power cable had been dragging through poison ivy. So at the end of the day, as he coiled the cord around his palm and elbow, he inadvertently launched a career-bending science experiment.

"Within 48 hours, I had your classic case of poison ivy on my arm. And as a scientist, I said, 'This is interesting, how bad can it be? I'll just leave this untreated,' " he recalls, sheepishly. "In about two weeks, I had learned just how uncomfortable poison ivy rash could be."

Uncomfortable sounds like an understatement. Jelesko says he barely slept while fighting the urge to "claw my itching flesh off." Eventually, he went to his family doctor, who prescribed oral steroids.

The experience sparked years of research into a plant he calls a "familiar stranger." He has studied the chemical, urushiol, that triggers that tell-tale rash, and the plant's biology overall. The tricky thing about avoiding poison ivy, Jelesko says, is the plant is highly adaptable and can take many different forms in different environments.

"It's remarkable," he says, with a laugh. "There's just an enormous amount of things with this plant that are currently unknown."

Here he offers insights into how to recognize Toxicodendron radicans (the plant's scientific name) before you risk touching it — and what to do when it's too late.

Know the leaf shapes

The axiom, "leaves of three, let it be," is accurate, says Jelesko, but those leaves can come in many shapes, even on the same plant. You're safe if the plant has thorns — poison ivy doesn't, but it does sometimes have little pale green berries.

Same plant, many forms

Another tricky feature of the species that can trip up passers-by: Poison ivy plants can grow in many shapes and sizes. When mature vines climb up a tree, their shape can even mimic that of the host tree. Simply pushing aside an innocent-seeming branch could make you pay a few days later when the rash begins to well up.

Jelesko's latest research, which is not yet published, finds that, in cities, poison ivy tends to grow as a climbing vine, whereas out in the forest, most of the plants are ground-creeping vines. And poison ivy is much more prevalent in "landscapes modified by humans" than out in the middle of the woods.

What to do when the tricky plant wins ...

If you think you've touched a plant, or unfortunately know you have, follow these tips to alleviate the problem. Of course, prevention is the best route. John Jelesko now dons a Tyvek suit and two pairs of gloves when he's wallowing in poison ivy.

If you even suspect you brushed up against the plant, wash with soap and water within a few hours. This tends to prevent an outbreak in most people.

To confirm you touched poison ivy, you can try what's known as the "black dot test" — but proceed with caution! With gloved hands, tear the leaf in half, put the sap on a piece of white paper. If it's poison ivy, the urushiol oil will turn black in 30 minutes. This is the same reason black dots appear on some of the plants.

Keep an eye out for a streaky, red rash in the first few days, especially if you've had a poison ivy reaction before. For poison ivy newbies, the rash could take a week to develop. Repeat customers can start breaking out in a day or two. Rather than building immunity, multiple exposures can make someone more sensitive, priming the immune system to produce a more "robust" response, Jelesko says.

When a rash appears, dermatologists recommend soothing it with anti-itch or corticosteroid cream.

And if it gets really bad, go to the doctor, especially if the rash involves sensitive areas like the mouth or genitals.

Steroids and anti-itch medicine don't always solve the whole problem and medicine has little else to offer. (If you're still in agony, cold compresses or a bath with oatmeal may help soothe your skin.) But more medical help may be on the way: Scientists are in early days of exploring new treatments. A researcher at Duke University found that part of the body's response involves an inflammatory protein "exciting" the nerve fibers in the skin and sending itchy signals to the brain. An antibody that counteracts the protein is currently in a clinical trial with humans.

If your pup came along with you on the outing that exposed you to poison ivy, never fear. Dogs are not allergic — but their fur can definitely hold the oil and transfer it to their owner, so have care with petting your dog after hiking past poison ivy. Scientists haven't found many animals that break out like humans do, though lab mice seem to be allergic enough for research.

And just in case you weren't disturbed enough by the proliferation of this itch-inducing vine, behold and be amazed by this king of the forest, a vine that's truly awe-inspiring in size. Happy hiking!

This story is part of a reporting partnership with NPR, Nashville Public Radio and Kaiser Health News. You can find Blake Farmer at @flakebarmer on Twitter.