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Controlled study links wild swimming to skin rashes and stomach bug risks

Researchers found higher rates of skin complaints and E. coli-linked gastrointestinal illness among open-water swimmers in Hungary, prompting calls to revise safety guidelines.

Updated Aug 27, 2026 · 05:17 UTC1 reports

The short version

  • A controlled study of 2,368 participants in Hungary found that wild swimmers were more than twice as likely to develop skin problems compared to non-swimmers.
  • While general swimming was not statistically linked to stomach bugs, bathers exposed to higher levels of E. coli and somatic coliphages faced a significantly higher risk of gastrointestinal illness.
  • The findings challenge World Health Organization guidelines that prioritize enterococci over E. coli for monitoring pollution levels in freshwater bathing sites.
  • Researchers plan to investigate alternative causes for skin irritation, as symptoms were not linked to traditional indicators of fecal pollution.

Key facts

  • In a controlled study involving 2,368 participants across four locations in Hungary, 2.7% of swimmers developed skin complaints compared to 1.3% of non-swimmers.[The Guardian]
  • Gastrointestinal illness was reported by 2.1% of swimmers compared to 1.9% of non-swimmers, with illness risk rising alongside higher concentrations of E. coli and somatic coliphages.[The Guardian]
  • Researchers found that enterococci levels were not associated with an increased risk of illness, contradicting WHO guidance that dropped E. coli as a freshwater monitoring standard in favor of enterococci.[The Guardian]
  • All four Hungarian sites utilized during the study complied with European Union bathing-water standards at the time of testing.[The Guardian]

What remains uncertain

  • The precise cause of skin rashes remains unknown, as symptoms showed no statistical link to markers of fecal contamination.[The Guardian]
  • The study was conducted over single-day trials at each location, and some participants reported swimming at other unmonitored sites during the follow-up period.[The Guardian]

Sources