Condition guide
Swimmer's Itch: What It Is and How to Treat It
Swimmer's itch (cercarial dermatitis) is an itchy, bumpy rash caused by a harmless-to-humans parasite larva found in some lakes and coastal waters. The larvae burrow into the skin and die there, and your body's allergic reaction is the itch. It typically appears within minutes to hours of swimming — as tingling, then small red bumps or blisters on skin that wasn't covered by a swimsuit. It's uncomfortable but self-limited, and there's a lot you can do to calm it down.
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What it is
Understanding swimmer's itch
- It's an allergic skin reaction to microscopic larvae (from parasites that normally live in birds and snails) — the larvae can't survive in people, so the infection doesn't spread inside you.
- It only affects skin that was exposed to the water, which is why the rash spares the area under a swimsuit.
- It's not contagious from person to person, and repeated exposures tend to produce a stronger reaction.
Symptoms
- Tingling, burning, or itching within minutes to hours of leaving the water
- Small reddish pimples, sometimes turning into tiny blisters, over the next 12 hours
- Intense itching that peaks in the first couple of days
- Bumps only where skin was uncovered — not under the swimsuit
What helps
Treating swimmer's itch at home
- 1Don't scratch — it prolongs the rash and can cause infection.
- 2Cool compresses, calamine lotion, and over-the-counter 1% hydrocortisone cream ease the itch.
- 3An oral antihistamine can help, especially at night.
- 4Colloidal-oatmeal or Epsom-salt baths are soothing.
- 5Prevention: towel off briskly right after swimming, and rinse off — larvae penetrate as the water evaporates on your skin.
When to see a doctor — or call 911
- Signs of a skin infection from scratching: increasing redness, warmth, pus, or a fever.
- A severe, widespread reaction, or swelling beyond the rash itself.
- Itching or a rash that isn't improving after about a week.
This page is general information, not a substitute for a medical evaluation. If you think you're having an emergency, call 911.
How Vacation Medicine helps
See a real doctor today — from wherever you are.
- A board-certified physician can confirm it's swimmer's itch and rule out look-alikes over a same-day video visit.
- For a severe reaction, they can prescribe a stronger topical or oral treatment for the itch and inflammation, sent to any pharmacy.
- If scratching has caused a skin infection, they can start the right treatment — and if it needs hands-on care, we'll say so and the visit's free.
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Swimmer's Itch, answered.
How long does swimmer's itch last?
The rash usually fades within about a week. The itch is worst in the first day or two and then eases.
Is swimmer's itch contagious?
No. The larvae die in your skin and can't spread to other people or to other parts of your body.
When should I see a doctor for swimmer's itch?
If the itch is severe, the rash is spreading or not improving after a week, or you see signs of infection (pus, warmth, fever), a physician can help — often with a same-day online visit.
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