Why do I get a rash after swimming in lakes?
Last updated September 3, 2026.
The classic answer is swimmer's itch: flatworm larvae from snails, meant for waterfowl, burrow into your skin by mistake and die there - and your immune system raises the itchy allergic bumps on every water-exposed patch (skin under your swimsuit is typically spared). It looks dramatic and is self-limited: resolves in days to a couple of weeks, not contagious, does not spread. Prevention: rinse and towel briskly right after swimming - dislodging larvae before they burrow is the real defense. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What to do
- Rinse and towel off briskly after lake swims: larvae dislodged before burrowing cause no rash.
- Treat the itch: cool compresses, calamine, antihistamine.
- Expect days, not weeks: self-limited, no scarring, not contagious.
- Get seen if: fever, spreading redness, or pus appear - that is infection, not swimmer's itch.
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