Parents Room

Here They Come: The Poison Plants of Summer

Spring has sprung, and summer is around the corner. You know the signs. Dad fires up the grill, oil companies raise gas prices, and kids come down with itchy rashes. The poison plants are back, and this summer they promise to send two million Americans to the doctor’s office.

The three most common culprits–poison ivy, poison oak, and poison sumac–are native to the Americas. European explorers hadn’t seen them before. Sometime around 1600, Captain John Smith recorded his encounter when he wrote, “The poisoned weed is much in shape like our English ivy, but being touched, causeth redness, itching, and lastly, blisters.”

Pocahontas could have warned him. After all, Native Americans knew all about poison ivy. Indian warriors coated their arrow tips with it, and medicine men rubbed the leaves on infections in an effort to break open the swollen skin.

Colonial doctors paid attention. They jumped on the poison ivy bandwagon and expanded its use to the treatment of herpes, eczema, arthritis, warts, ringworm, and even rattlesnake bites. Use of poison sap in early American medicine was so widespread that poison oak was listed in the Pharmacopoeia of the U.S. as an official therapeutic agent.

Today we know the rash of poison plants is a contact dermatitis. Upon first exposure, most folks develop antibodies against the sap. On subsequent exposure, the antibodies attack the sap, resulting in the bothersome rash. The few who don’t make antibodies, won’t get the rash. But they should still watch out–antibody production can begin anytime, making a fool out of poor Uncle Pete a day or two after he rubs poison ivy up and down his arm just to prove he ain’t allergic.

So what is poison sap anyway? The offending chemical is urushiol, a yellowish oil inside the leaves, stems, and roots of the poison plants. Because it’s inside the plant, undisturbed leaves won’t harm you. However, if the leaves are chewed by insects, stepped upon, or otherwise damaged, the oil leaks onto the plant’s surface where it can come into contact with human or animal skin. As it turns out, only humans and closely-related primates break out with the rash. Dogs, cats, cattle, and sheep are not affected, but they can convey the oil to their human keepers. Clothing and tools also spread the oil, and since the sap remains allergenic for years, unsuspecting spring gardeners can get the rash from last season’s gloves.

If you come into contact with poison sap, or at the first sign of rash, you should take a long shower with plenty of soap and water. Avoid immersing in a bath because the oil can float, spreading to other parts of your body. Washing the oil from your skin will stop further spread. Rash may still appear in new areas, but this is because areas exposed to smaller amounts of sap take longer to break out.

Once you have the rash, it stays awhile. The skin has to repair itself, a process taking 10-14 days. All you can do in the meantime is treat the symptoms. With mild cases, over-the-counter hydrocortisone cream and oral antihistamines–like Benadryl–is the best combination to control inflammation and itching. If you have widespread rash, face involvement, or infected blisters, it’s time to see your doctor. You might need steroid pills, a shot, or an antibiotic.

As always, prevention is best. All three poison plants have compound leaves with three leaflets. My grandma used to say, “Leaves of three? You let them be!” and she was right. The leaves are glossy green with a smooth surface. In the fall, the foliage may turn orange or scarlet. Poison ivy is a stout weedy vine that often climbs trees. Poison oak is larger and more shrub-like. Poison sumac grows in swampy areas and can reach up to twenty feet in height.

There is a medicine that prevents the rash by providing a barrier on the surface of exposed skin. IvyBlock (bentoquatam) is available over the counter and approved for age six and up. It should be applied 15 minutes before exposure and reapplied every 4 hours for continued protection.

So get out there and enjoy the Spring. Grill your burger. Fill your tank. Take a ride in the country. But when you get there, remember what my grandma said. Otherwise, you might end up in the waiting room, scratching your sores with those other two million Americans.

Mike Patrick Jr, MD is an American Pediatrician
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