Beware: Toxic Plants Are Out to Get You

By Eva Briggs, M.D.

I almost made it through summer this year without poison ivy — but not quite.

A late August thunderstorm blew down many trees along the Erie Canal towpath where I ride my bike. I had to lift my bike over trees and step over. I’m pretty sure that in the process I brushed against poison ivy. I finally had to seek medical care for a prescription to treat the itching and oozing.

Poison ivy and its relatives (Toxicodendron species including poison oak, poison sumac) cause a skin reaction due to the oil urushiol. These are not the only plants out there able to harm you by touch alone.

Stinging nettle — scientific name Urtica dioica — is common in this region. It is originally native to Europe and parts of North Africa and Asia. It now grows worldwide. The stems and leaves are hairy. Some of those hairs, called trichomes or spicules, act like tiny hypodermic needles. If you brush against them, these hairs detach and inject chemicals that cause stinging and burning. The irritatant chemicals include histamine, serotonin, acetylcholine and more. Treatment is topical antihistamines or steroids.

My experience has been that although nettles sting like crazy, the pain and rash resolve on their own in a few hours even if not treated. It doesn’t last days or weeks like untreated poison ivy.

The internet indicates that nettles can be cooked and eaten, but I sure don’t plan to try that. There is even World Nettle Eating Championship in the United Kingdom whose contestants have to eat raw nettles! As far as I’m concerned, no thanks!

Phytophotodermatitis is a rash that develops when the juices of certain plants drip onto the skin which is then exposed to sunlight. The offending chemicals are called furanocoumarins. The exposed areas turn red and sometimes blister. It’s not an allergic reaction; it’s a chemical reaction. After the initial phase subsides, the area can be persistently dark, called hyperpigmentation. This phase isn’t painful, but the discoloration can last for moths.

Citrus juices, especially lime, are a common cause. In fact, a nickname for people who develop this after a tropical vacation is margarita dermatitis. The rash often forms a streaky pattern from dripping juices. Other common plant culprits include celery, figs, wild parsnips, dill and carrots. It’s been reported from some Chinese herbal medicines. The plant giant hogweed, Heracleum mantegazzianum, can trigger a dangerously strong form of phytophotodermatitis that may lead to scarring or blindness if the plant juices are rubbed or splashed into the eyes.

Mango, Mangifera indica, also can cause allergic contact dermatitis from chemicals in the mango skin. I found this out years ago when visiting my daughter in Australia. Mangoes there were relatively inexpensive, abundant and deliciously ripe. So, we ate them pretty much every day. I developed a rash similar to poison ivy on my hands from handling all those mangos. But they were so delicious that it was worth it.

Rosin or colophony, is a chemical produced in the sap of pine and spruce trees. It’s found in many products: cosmetics, adhesives, medicines, toiletries, some household cleaners, sport racquet handles, to treat stringed instrument bows, chewing gum, firewood and more. Symptoms are redness, irritation, blistering and intense itch. It usually starts 1-4 days after exposure. Like poison ivy, it’s treated with topical steroids and if severe with oral steroids, as well as avoidance.

Poison ivy isn’t the only plant that’s out to get you!