Swimmer's itch is an itchy rash that can occur after you go swimming or wading outdoors. Also known as cercarial dermatitis, swimmer's itch is most common in freshwater lakes and ponds, but it occasionally occurs in salt water.
Swimmer's itch is an allergic reaction to microscopic parasites that burrow into your skin. The parasites associated with swimmer's itch normally live in waterfowl and some animals that live near the water. Humans aren't suitable hosts, so the parasites soon die while still in your skin.
Although uncomfortable, swimmer's itch is usually short-lived. The rash typically clears up on its own within a few days. In the meantime, you can control itching with over-the-counter or prescription medications.