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.
Can swimmer's itch be spread from person-to-person?
Who is at risk for swimmer's itch?
Anyone who swims or wades in infested water may be at risk. Larvae are more likely to be swimming along shallow water by the shoreline. Children are most often affected because they swim, wade, and play in the shallow water more than adults. Also, they do not towel dry themselves when leaving the water.
Once an outbreak of swimmer's itch has occurred in water, will the water always be unsafe?
No. Many factors must be present for swimmer's itch to become a problem in water. Since these factors change (sometimes within a swim season), swimmer's itch will not always be a problem. However, there is no way to know how long water may be unsafe. Larvae are generally infective for 24 hours once they are released from the snail. However, an infected snail will continue to produce cercariae throughout the remainder of its life. For future snails to become infected, migratory birds or mammals in the area must also be infected so the lifecycle can continue.
What can be done to reduce the risk of swimmer's itch?
- Avoid swimming in areas where swimmer's itch is a known problem or where signs have been posted warning of unsafe water.
- Avoid swimming near or wading in marshy areas where snails are commonly found.
- Towel dry or shower immediately after leaving the water.
- Encourage health officials to post signs on shorelines where swimmer's itch is a current problem.
- Do not attract birds by feeding them in areas where people are swimming.
Is my swimming pool safe to swim in?
Yes. As long as your swimming pool is well-maintained and chlorinated, there is no risk of swimmer's itch.
Portions of the above information have been provided with the kind permission of the Center for Disease Control and Prevention. (www.cdc.gov).
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Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care June 22, 2017