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Poison Ivy, A ‘Familiar Stranger’ That Could Ruin Your Summer


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

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

The Virginia Tech associate 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 recalled, sheepishly. “In about two weeks, I had learned just how uncomfortable poison ivy rash could be.”

Uncomfortable sounds like an understatement. Jelesko said 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 telltale rash and the plant’s biology overall.

The tricky thing about avoiding poison ivy, Jelesko said, is the plant is highly adaptable and can take many different forms in different environments.

“It’s remarkable,” he said, 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 scientific name of the plant, before you risk touching it — and what to do if it’s too late.

Know The Leaf Shapes

The axiom “leaves of three, let it be” is accurate, said 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 white berries.

Can You Recognize This Leaf?

All of these are the same pesky, rash-inducing plant. Poison ivy leaves sometimes appear with jagged or lobed edges, and sometimes smooth.

(Clockwise from top left) Poison ivy with smooth edges; jagged edges; round leaves; notched leaves. All pictures were taken on a trail in a state park on Tennessee’s Cumberland Plateau.
Credit: Blake Farmer/WPLN

Same Plant, Many Forms

Poison ivy can present as a vine or a shrub. 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 the passer-by pay a few days later, when a 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.

Some poison ivy vines can be downright awe-inspiring in their size, like the one in this video.

Poison ivy can grow as a creeping vine on the ground.
Credit: Blake Farmer/WPLN

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. For John Jelesko, he now dons a protective Tyvek suit and two pairs of gloves when he wallows in poison ivy. Your last line of defense:

  • Wash with soap and water within a few hours. This tends to prevent an outbreak in most people.
  • Keep an eye out for a streaky, red rash in the first few days, especially if you’ve previously had a reaction to poison ivy. 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 said.
  • 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.
  • But steroids and anti-itch medicine doesn’t solve the whole problem. Aresearcher at Duke University found that part of the body’s response involves a protein known for inducing inflammation on the skin, “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 to determine potential side effects.
  • 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 owners, so pet your dog with caution 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.

This story is part of a partnership that includes Nashville Public RadioNPR and Kaiser Health News.

Kaiser Health News (KHN) is a national health policy news service. It is an editorially independent program of the Henry J. Kaiser Family Foundation which is not affiliated with Kaiser Permanente.


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