What You Need to Know About Swimmer's Itch

Clinically known as cercarial dermatitis, swimmer’s itch is an allergic reaction to a parasitic worm that resides is both fresh and saltwater bodies. When the worm encounters human skin while looking for a host, it can cause some uncomfortable symptoms. Luckily, the condition is mostly an annoyance and should resolve itself after a short time.

The parasite that causes swimmer's itch normally live in aquatic mammals such as beavers, or birds like ducks and geese. When the animal excretes feces into a lake or pond, the parasite's eggs disperse as well and eventually hatch. The young larvae, called miracidia, seek out their intermediate host — a type of aquatic snail — where they reside until maturity.

The cercariae parasite infection on human skin is accidental. The mature cercariae are excreted by the snail and immediately begin seeking out a waterfowl or mammal as their next host. Anyone wading in the water during this phase of the cycle will be an attractive potential host to the indiscriminate parasites, who will embed themselves in the skin.

Because humans are inappropriate hosts, when the cercariae penetrate exposed skin, they usually cause immediate irritation and itch due to the body’s immune response. Sometimes, the itchiness will subside and resurface within the next 24 hours, along with a rash. Cercarial dermatitis looks like raised red welts on the skin. The length of time in the water is directly related to the intensity of symptoms.

While there are no major complications from swimmer’s itch, there are a couple of cautionary points to keep in mind. Firstly, if blisters develop, visit a dermatologist immediately. While swimmer’s itch is likely to clear up in a week or so, blistering may lead to scarring, which could take longer to resolve or leave unwanted marks. Secondly, the severity of the immune response varies from person to person. Those who have experienced swimmer’s itch before will have a quicker immune response the next time.

It’s natural to scratch an itch, but in this case, doctors caution against it. Vigorous scratching can break the skin and lead to bacterial infection. To help relieve the itching, apply an over-the-counter anti-itch lotion or cream, or cover the affected area with a paste of baking soda and water. Studies show that sodium bicarbonate eases the inflammation that accompanies many dermatological conditions.

One way to relieve swimmer’s itch is to place a cold compress over the irritated area; the coolness will relieve the inflammation that causes burning and itching. If the itching is more widespread, a warm Epsom salt bath can offer relief. Epsom salts are generally considered safe to use; start with a low concentration of 1.5 cups for every gallon of water. Soak for 15 minutes.

While anyone can get swimmer’s itch, children are more prone to the infection. They tend to play in shallow water and are less conscientious about showering off afterwards. Unfortunately, young people are also more likely to develop complications such as fever or a rash, which may last longer than the usual few days. If a child has any of these symptoms, seek medical attention immediately.

When it comes to swimmer’s itch, the best way to reduce one's risk is to avoid areas where the parasite might reside. Be conscious of where you swim or wade, and check reports about outbreaks. Cercariae love warm water, so it’s best to head out to deeper, cooler water and stay away from the shore. Most importantly, rinse with clean water after swimming and dry yourself off properly to reduce the risk of dermatitis. Sunscreen can also provide a protective barrier against the parasite.

Over the past few years, cases of cercarial dermatitis have increased worldwide, with spikes specifically in South America, Asia, and the Southwest U.S. This has led researchers to label swimmer’s itch an emerging disease. What's more concerning is that studies on rats show the parasite may become better at penetrating the skin over time and could find its way inside the body or become a worse infection. For example, during the early 20th century, Japanese lakeside disease or Koganbyo was a prevalent and severe form of cercarial dermatitis that afflicted rice farmers.