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Swimmer's Itch

What is swimmer's itch?

Swimmer's itch, also called cercarial dermatitis, is a skin rash caused by an allergic reaction to infection with certain parasites of birds and mammals. These microscopic parasites are released from infected snails who swim in fresh and salt water, such as lakes, ponds, and oceans used for swimming and wading. Infection is found throughout the world. Swimmer's itch generally occurs during summer months.

What are the signs and symptoms of swimmer's itch?

Within minutes to days after swimming in contaminated water, you may experience tingling, burning, or itching of the skin. Small reddish pimples appear within 12 hours. Pimples may develop into small blisters. Itching may last up to a week or more, but will gradually go away.

Because swimmer's itch is caused by an allergic reaction to infection, the more often you swim or wade in contaminated water, the more likely you are to develop more serious symptoms. The greater the number of exposures to contaminated water, the more intense and immediate symptoms of swimmer's itch will be.

Be aware that there are other causes of rash that may occur after swimming in fresh and salt water.

Do I need to see my health care provider for treatment?

No. Most cases do not require medical attention.

If you have a rash, you may try the following for relief:

• corticosteroid cream
• cool compresses
• bath with baking soda
• baking soda paste to the rash
• anti-itch lotion
• Calamine* lotion
• colloidal oatmeal baths, such as Aveeno*

Try not to scratch. Scratching may cause the rash to become infected. If itching is severe, your health care provider may prescribe lotion or creams to lessen your symptoms.

How does water become infested with the parasite?

The adult parasite lives in the blood of infected animals such as ducks, geese, gulls, swans, as well as certain aquatic mammals such as muskrats and beavers. The parasites produce eggs that are passed in the feces of the infected birds or mammals.

If the eggs land in the water, the water becomes contaminated. Eggs hatch, releasing small, free-swimming larvae. These larvae swim in the water in search of a certain species of aquatic snail.

If the larvae find one of these snails, they infect the snail and undergo further development. Infected snails release a different type of larvae (cercariae, hence the name cercarial dermatitis) into the water. This larval form then searches for a suitable host (bird, muskrat) so they can start the lifecycle over again. Although humans are not a suitable host, the larvae burrow into the skin of swimmers, which may cause an allergic reaction/rash. The larvae cannot develop inside a human and they soon die.