The cause of swimmers’ itch is an allergic reaction to parasites that migrate from snails to ducks, geese, gulls, swans, muskrats and beavers. The parasites then return to water through infected feces and eggs.
Swimmers’ itch isn’t contagious from person to person. You don’t need to worry about “catching” swimmers’ itch from someone who has the itchy rash.


Swimmers’ itch is an itchy rash caused by certain parasites that normally live on waterfowl and freshwater snails. On warm, sunny days, especially in calm freshwater lakes or ponds, these parasites can be released into the water. During your swim, these parasites might burrow into your skin, where they cause the swimmers’ itch rash. Humans aren’t suitable hosts for these parasites, so the parasites soon die.

Although uncomfortable, swimmers’ itch is usually short-lived. The rash of swimmers’ itch, also called cercarial dermatitis, typically clears up on its own within a few days. In the meantime, you can control itching with over-the-counter or prescription medications. If symptons persist, consult your doctor.

What are the symptoms of swimmer’s itch?

Sensitized people get swimmer’s itch when the cercarial stage (originating in specific snail species) accidentally enters their skin. Usually within 30 minutes, a small red spot appears at the site where the cercaria penetrated.

This red spot will continue to increase in size for the next 24-30 hours. The raised, reddened spot is now called a papule. It will continue to itch for up to a week. Papules are limited to areas of the body that get exposed to water because cercariae can not live out of the water. For a few species of parasites that cause swimmer’s itch, toweling off may help. For most species however, toweling off may be ineffective because the cercariae penetrated the skin while the person was in the water.

If swimmer’s itch occurs on a lake, does that mean that the lake is polluted?

No, the opposite is probably true. Natural lake conditions promote the diversity of species, including the birds and snails that are potential hosts for the swimmer’s itch parasite.