Last year when putting in my dock, I was attacked by what I presumed were bugs. I was at first terribly itchy; I was left with a rash, which morphed into spots within a couple of days. The itching became a burning sensation. I now think aquatic plants were responsible. Do your experts have an opinion as to the culprit?—Tom Scanlan, Lake St. Peter, Ont.
Even though we sent your photo—which was too gross to print in these pages, no offense—to several medical experts, we couldn’t get anyone to suggest a culprit. Doctors aren’t keen on diagnosing a rash based only on a photo. And they’re really not keen on diagnosing someone who isn’t a patient. (As one doc we asked put it: “This is not an appropriate way to seek medical advice!”)
But—assuming whatever caused the rash was in fact something in the lake, and not an unrelated reaction to, for example, sunscreen or a new laundry detergent—it probably wasn’t from a plant. “There are no obvious aquatic plants that would cause a reaction like that,” says Vicki Simkovic, the coordinator for the Ontario Invasive Plant Council. “In Ontario, aquatic plants typically do not cause rashes. They’re not the same as terrestrial plants, such as poison ivy or giant hogweed.”
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We’re no dermatologist, but we have answered many, many Cottage Q&As. Our immediate thought was, Hey, maybe that’s swimmer’s itch. It fits with your symptoms, and your rash.
“It certainly resembles swimmer’s itch, much more than a plant-induced rash,” says Tim Geary, an emeritus professor with the Institute of Parasitology at McGill University in Montreal. Swimmer’s itch (a.k.a. cercarial dermatitis) is caused by the larvae of schistosome tremadtodes when they burrow into your skin. Horrifying! But not dangerous. They use waterfowl and marine mammals as hosts, and, despite their best burrowing efforts, they can’t form any long-lasting parasitic relationship with you. The larvae quickly die, but not without leaving you with a parting gift: an allergic reaction that begins as a tingling or prickling sensation and turns into mosquito-bite-like bumps 12 to 24 hours later. The best prevention against swimmer’s itch—other than avoiding the water—is to towel off right away. The larvae don’t attempt to burrow under the skin until you’re out of the lake, says Geary.
What bit me?
None of our experts denied that you had cercarial dermatitis. But nobody confirmed it either. “Rashes from swimming in lakes and ponds are common,” says Anne Ellis, a professor in the department of medicine at Queen’s University in Kingston, Ont. “There are multiple possible causes.” (Side note: just because your lake experienced a swimmer’s itch outbreak one year, it doesn’t mean you’ll have the same problem the next. Lots of factors can affect the larvae population.) Either way, if you get this mystery rash again, Ellis recommends treating it with a non-drowsy antihistamine and topical corticosteroids.
Got a question for Cottage Q&A? Send it to answers@cottagelife.com.
This article was originally published in the March/April 2024 issue of Cottage Life.
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