Swimmer’s itch can quickly ruin a pleasant day at the beach

Learn how to avoid this painful skin rash.

If you live or vacation in Michigan, it’s likely you have heard of, or personally experienced, an uncomfortable skin rash suffered by individuals after swimming in an inland lake. Swimmer’s itch, or schistosome cercarial dermatitis, is an allergic reaction that occurs when the larval (cercarial) stage of certain parasitic flatworms from the Schistosomidae family burrow into a person’s skin. As part of their life cycle, these flatworms require a snail host and a vertebrate host. The vertebrate host is usually a bird but can be rodents such as mice or muskrats. Common mergansers, mallards, Canada geese, swans, grackles, and red-winged black birds have all been confirmed as common vertebrate hosts.

As the larva hatch and leave the snail, they swim quickly in search of one of their new host as most larva can only survive about 24 hours and will not live out of water. When larvae encounter individuals swimming or playing in shallow water along the shore, they may burrow into exposed skin as they search frantically for a vertebrate host. Because humans are not a suitable host, these tiny larva die after piercing your skin. Transparent and less than 1/32 inch in length, they can’t be seen without a microscope.

At first, an affected person may feel a tingling, burning, or itching of skin that was directly exposed to the lake water. Soon, often within 30 minutes, a small red spot appears at each site of entry. The spots continue to increase in size for about 24 hours and cause intense itching. Itching may continue for a week gradually decreasing in severity. The rash may be mistaken for mosquito bites, chiggers, chicken pox, impetigo, or thought to be the result of touching poison ivy or stinging nettles. Fortunately, the rash is not contagious.

Though swimmer’s itch was first identified in 1928 at Douglas Lake Cheboygan County, nearly every state, Canada, and over 30 countries in Europe, Asia, and Africa have since reported incidences of a similar swimming-related skin rash. Both fresh water and marine, or salt water, varieties of parasites are known to cause the uncomfortable rash. You may hear swimmer’s itch called duck rash, clam digger’s itch, pelican itch, or another name in various parts of the U.S. and in other countries.

How does one avoid swimmer’s itch?

  • Before swimming, create a water-proof barrier by applying baby oil, creams containing DEET, Swimmer’s Itch Guard, or similar products on exposed skin to prevent the larvae from burrowing.
  • After swimming, vigorous towel off body parts that were directly exposed to the lake water.
  • Avoid swimming in shallow shoreline water where snails tend to be and when winds are onshore which cause the larva to congregate along the shoreline.

How is swimmer’s itch treated?

  • Apply corticosteroid cream, anti-itch lotion or a baking soda paste to affected areas.
  • Soak in baths containing Epsom salts, baking soda, or colloidal oatmeal.
  • Avoid scratching affected areas as that may cause a secondary infection. If the itching is severe or infection occurs, consult your physician for a prescription.

Some people are sensitive to the burrowing larva while others may not have a reaction. A more severe reaction can occur with repeated exposures to the larva. Children, rather than adults, are more inclined to be victims as they often play in shallow waters near the shoreline and are not vigilant about toweling off when leaving the water.

How can you help prevent swimmer’s itch from becoming established in your lake?

Don’t feed birds and establish a green belt along your shoreline of native plants to discourage them from congregating on your property. The shade from the green belt will also reduce the amount of bottom-dwelling algae, the primary food for the snails. If you have a lake association, encourage them to educate members about swimmer’s itch and institute control measures.

For more information about swimmer’s itch, the Michigan Department of Environmental Quality offers a webpage with several resources including an excellent bulletin about the situation in Michigan.

Visit the Michigan State University Extension website to learn more about aquatic invasive species, shoreline protection, and many other topics.

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