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What Causes Swimmer's Itch?

Schistosome cercarial dermatitis -- known to most people as swimmer's itch -- is a short-term skin rash that strikes some people after they have gone for a swim. The rash caused by swimmer's itch irritates the skin, causing it to become red and inflamed. The rash has a similar effect to poison ivy, in that the skin in inflicted areas develops pustules that itch intensely.

  1. A Parasite

    • Swimmer's itch is caused by a parasite that typically is borne by birds, some mammals and snails. It is from snails that the parasite typically enters fresh water lakes and ponds. The snails carry the parasite to the water, where it migrates during its life cycle. Waterfowl and semi-aquatic mammals then in turn carry the parasite to other parts of a body of water -- or to an entirely different lake or pond -- after coming into contact with it.

    Under the Skin

    • Once the parasite is in the water, humans are susceptible to it, particularly late in the spring when waters have started to warm up and the parasite proliferates. A person, however, is able to be stricken with swimmer's itch at any time of the year. The parasite works its way under the epidermal layer of the skin in humans; once there, it dies. While there are no permanent side effects, the parasite causes a short-term allergic skin reaction.

    Air Drying a No-no

    • Contact with the parasite does not ensure a person gets swimmer's itch; only about one-third of people who encounter the parasite have an allergic reaction. Most susceptible are swimmers who air dry after a dip, rather than drying off with a towel, which brushes the parasites off the body. Children also are more susceptible to swimmer's itch than adults, in part because they stay closer to shore, where the parasite is most often found, and also because they tend to stay in the water longer than adults, increasing their risk of encountering the parasite. Swimmer's itch, unlike viruses and other diseases, does not spread from person to person.

    Short Lived, but Highly Irritating

    • Once the parasite works its way under the skin, symptoms are observed within periods as short as one or two hours. The rash is maddeningly itchy, in much the same manner as poison ivy or being stung by a swarm of insects, and the pustules it forms break open when scratched. Fortunately for most people, an attack of swimmer's itch is usually over within five to seven days. Those who have suffered an attack of swimmer's itch, however, are more prone to be struck with it again in the future.

    Avoidance

    • There are no guaranteed ways to avoid swimmer's itch when swimming in fresh water, but there are steps that are taken to reduce the likelihood of it developing. Always towel dry after a swim; avoid areas where you see snails or where waterfowl congregate; and swim in deeper water if possible.

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