Cercarial dermatitis, also known as swimmer's itch, is an itchy rash that occurs most commonly after swimming or wading in shallow areas of freshwater lakes and ponds. It may also occur after swimming in salt water.
Cercarial dermatitis is an allergic reaction to tiny parasites that live on water birds and other animals that live near water (geese, ducks, muskrats, beavers). They can attach to humans and burrow into the skin; however, because humans do not make good hosts for the parasites, they die within a few days typically. The rash also generally resolves in a few days. The rash may begin minutes up to days after swimming in infested water and looks like reddish pimples or blisters on exposed skin. Continued exposure to the parasites can make the rash worse. Avoid scratching the rash to prevent infection. Cercarial dermatitis is not contagious; therefore, you cannot catch it from someone that is affected. Please see your doctor or a dermatologist if you have similar symptoms after swimming.