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Swimmer’s Itch: Prevent and Treat It

July 24, 2011

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Every spring we welcome a few passing ducks and geese to our small backyard pond. Often a pair or two will hang around for a few weeks.

When the water gets warm enough for swimming, I know I’ll need to take preventive measures before and after my frequent midsummer swims to keep from getting a bad case of swimmer’s itch.

Once you’ve had a case of raised rash that can itch for a couple of weeks (a lot like poison ivy), you won’t want to get it again.

The cause? The larval, aquatic form of a flatworm whose life cycle involves both snails and (in most cases) birds. [If your computer has a Flash player, you can see an animated simulation of the organism’s life cycle.]

Cases have occurred in every state in the U.S. and all the Canadian provinces, most of them in the northern tier of states.

People who get it tend to swim regularly, have sensitive skins, and wade or hang out in shallow water (especially kids), since the parasites tend to concentrate near the shoreline.

The flatworm larvae cause an allergic reaction, but because humans aren’t a suitable host for the worms, they die without infecting you.

The rash shows up any time from a couple of hours to two days after exposure. On me, anyway, it looks a lot like a poison-ivy rash. Vigorous scratching can lead to infection.

The rash can get more severe each time you get it. But it’s never contagious. You can’t give it to or get if from others.

If you get a bad case of swimmer’s itch, soak in a tepid oatmeal bath. For just a few spots, spritz on apple cider vinegar or swab with a damp washcloth dipped in baking soda.

To prevent swimmer’s itch:

  • Try to avoid swimming in areas where lots of ducks and/or geese congregate (usually because people are feeding them), or near marshy areas that may harbor lots of snails.
  • Slather on the “waterproof” sunscreen before you send your kids into lakes and ponds. It seems to help prevent the flatworms from penetrating the skin. 
  • Shower right after swimming, if possible. If you can’t (or even after you do), rub down vigorously all over with a rough towel.

For more information, visit the CDC Swimmer's Itch frequently-asked-questions page.

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Margaret Boyles lives in a wood-heated house in central New Hampshire. She grows vegetables, eats weeds, keeps chickens, swims in a backyard pond in summer, snowshoes in the surrounding woods in winter, and commutes by bike whenever possible.

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