Swimmer's Itch: What Causes the Rash, How to Lower Your Risk and Soothe It
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How we wrote this: A plain-English summary of the CDC's swimmer's itch page (September 10, 2024), checked October 29, 2026. This is general information, not medical advice.
Itchy red bumps after a lake or ocean swim may be swimmer's itch, also called cercarial dermatitis.
What causes it
The CDC says it's an allergic reaction to microscopic parasites that normally infect birds and some mammals, such as ducks, geese, gulls, swans, muskrats and raccoons. The parasites' eggs reach the water in animal droppings and hatch into larvae that infect certain aquatic snails. Infected snails release another larval form into fresh or salt water. If those larvae land on a person instead of a bird, they burrow into the skin and cause the rash. People aren't a suitable host, so the larvae soon die.
It's not contagious from person to person. A well-maintained, chlorinated swimming pool carries no risk.
Symptoms
- Tingling, burning or itching within minutes to days after swimming,
- small reddish pimples within 12 hours,
- sometimes small blisters.
The itching can last a week or more but goes away. Each repeat exposure tends to bring faster, stronger reactions, because it's an allergic response.
Who's most at risk
Larvae gather in shallow water near the shore. The CDC says children are affected most often, because they play in the shallows and are less likely to towel off.
How to lower your risk
- Don't swim where swimmer's itch is a known problem or where warning signs are posted.
- Avoid marshy areas where snails are common.
- Towel dry or shower right away after leaving the water.
- Don't feed birds near swimming areas.
- Ask health officials to post signs where it's a current problem.
Soothing the rash
Most cases don't need medical care. The CDC lists home relief: corticosteroid cream, cool compresses, Epsom salt or baking soda baths, colloidal oatmeal baths, a baking soda paste and anti-itch lotion. Try not to scratch, because scratching can cause a bacterial infection. If itching is severe, a health care provider may suggest prescription products.
See also: harmful algal blooms, beach water quality, Vibrio infections.