What’s the ‘sitch’ on swimmer’s itch?

Swimmer’s itch is an allergic reaction to a parasitic infection – while it sounds frightening, it’s not nearly as serious as it sounds.

Red beach towel hanging in foreground with sandy beach and water out of focus in the background. For decorative purposes.
One prevention measure is to dry off immediately after enjoying a day at the lake. Photo credit: canva.com.

Itchy skin seems like an unavoidable outcome of summertime adventures. From mosquito bites and peeling sunburns to mysterious skin rashes, we’ve all experienced a bit of epidermal irritation during the dog days of summer. While dodging mosquitos and slathering on the sunscreen seem like second nature, what about avoiding the dreaded diagnosis of swimmer’s itch?

Swimmer’s itch is steeped in local folklore and the myths about what causes it are unfortunately mostly not true. While stories from unlucky itchy swimmers might sound scary, the symptoms aren’t quite as dramatic as the tales you may have heard. In reality, swimmer’s itch is a temporary skin rash caused by an allergic reaction to microscopic parasites that infect some birds and mammals.

While the word parasite might make your skin crawl, fear not: the itchiness and bumps that are the telltale signs of swimmer’s itch are not caused by a parasite actually living under your skin. In fact, they cannot survive in humans at all and die almost immediately upon burrowing into your skin.

How do waters become infested?

The parasite that causes swimmer’s itch has a fascinating and complex life cycle. The adult parasite lives in the blood of certain infected waterfowl and mammals, and produces eggs that are passed in feces. If the eggs land in the water, they hatch and release microscopic larvae. These larvae then search for specific host species of aquatic snails. If the larvae locate the specific snail species, it will infect it and multiply. The snail then releases a different type of microscopic larvae known as cercariae - hence why swimmer’s itch is also called cercarial dermatitis. Cercariae swim to the surface of the water looking for certain birds or mammals to continue its life cycle. While humans are not the intended host, cercariae may intercept an unsuspecting swimmer. One important thing to note about this intricate lifecycle is that it involves two specific host species. The presence of an infected bird does not mean swimmers itch will be present because it also requires the presence of a specific snail species. Both must be present in the same lake for the life cycle to be completed. And not all waterfowl, mammals, or aquatic snails may be infected.

Signs of swimmer’s itch

There are a few telltale ways to know if you have swimmer’s itch. The most common symptoms include small, red bumps that may have sporadic itching for a few days. They often resemble chigger or mosquito bites. Although uncomfortable, swimmer’s itch is not contagious or fatal. The allergic reaction that we have to swimmer’s itch is actually a reaction to the parasite, not the result of the burrowing itself.

Swimmer’s itch symptoms may occur while swimming or right when leaving the water. Swimmers may feel a small prick or itch when the larva burrows into their skin, but most of the time they will not notice anything is amiss until red bumps start to appear. Similar to poison ivy, some people are fortunate enough to have no reaction at all.

Preventing swimmer’s itch

There are a few steps that lake users can practice while enjoying Michigan’s water bodies to prevent swimmer’s itch. One is to avoid swimming in shallow, shoreline areas where snails congregate in greater numbers. Also, when wind is blowing toward the shore, it is more likely to bring in cercariae which float on the water’s surface so swim away from downwind areas. When exiting the water, rinse off with clean water and dry off with a towel immediately. And finally, some people have luck protecting their skin by creating a barrier with a water repellent substance like sunscreen.

Your activities on the shore can also impact the prevalence of swimmer’s itch. Avoid feeding waterfowl in swimming areas as an aggregation of waterfowl will lead to higher concentrations of hosts for the parasite. Additionally, maintaining a healthy shoreline with native plants prevents waterfowl from gathering nearshore and supports a healthier lake ecosystem. Utilizing these prevention steps should make your summers more enjoyable, and a little less ‘itchy’!

Several methods of waterfowl and snail control have been tested over time, but none are highly successful. One method is the usage of copper sulfate to eliminate the host snails. However, copper sulfate is a nonspecific poison and is toxic to many aquatic plants and animals. A permit is needed from the Michigan Department of Environment, Great Lakes, and Energy to apply copper sulfate. Other alternatives to copper sulfate have included trapping and relocating waterfowl, creating safe swim areas using floatable barriers, and using fine mesh nets to remove larva from a swim area. Despite these efforts, the best tool against swimmer’s itch is adjusting your behavior when swimming and leaving the water.

Learn more about swimmer’s itch and inland lakes

Learn more about swimmer’s itch and other topics related to lakes and wildlife at the virtual Michigan Inland Lakes Convention happening September 14-16, 2022. The three-day event will include more than 45 engaging presentations and workshops on current lake research, lake conservation, stewardship opportunities, policy, and regulations, and much more. The Convention is hosted in part by Michigan State University (MSU) Extension and is a program of the Michigan Inland Lakes Partnership, a collaboration of diverse organizations with a common mission to advance stewardship of Michigan's inland lakes.

A version of this article originally appeared in the June 2022 issue of the Lakefront Lifestyles Magazine.

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