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Public Health - Seattle & King County

Swimmer's itch facts

Swimmer's itch (cercarial dermatitis) is an itchy rash caused by a parasite in lake water. If water contaminated with parasites dries on a swimmer's skin, the microscopic parasites can burrow into the skin. Although the rash can be very uncomfortable, it is not serious and affects only the skin, not the rest of the body.

After burrowing into the skin, the parasite dies and the body reacts by forming red itchy bumps. The itching and rash generally go away within about 5 - 6 days. The parasites can not be spread from person to person. Affected individuals should consult with their health care provider if the symptoms become severe or if the rash worsens or appears to become infected. Signs of infection are increased redness, pain, swelling, warmth, and possibly fever.

duck in waterThe parasite that causes swimmer's itch is deposited into lakes via goose and duck droppings. The parasites then move into snails where they mature, eventually coming out to re-infect more waterfowl, and sometimes people.

Tips for reducing the risk of swimmer's itch include:

  • Liberally apply a waterproof sunscreen prior to swimming. There is evidence that this may provide some protection.
  • Briskly dry off with a towel as soon as you come out of the water, including the skin under the swimsuit.
  • Shower immediately if these facilities are available.
  • Stay immersed in the water--wading creates the highest risk for swimmer's itch.
  • Do not feed ducks and geese. This may attract more of these birds to the area and increase contamination of the water and shoreline.
  • Avoid swimming in marshy areas where snails are commonly found.

Visit the CDC's website on Swimmer's itch