Wild Swimming Raises Skin Rash and Gut Illness Risks, Study Reveals

A landmark controlled trial has shown that swimming in natural waters raises the likelihood of skin rashes and gastrointestinal illnesses.

Participants in the Hungarian sites were over twice as prone to skin complaints, and higher levels of E coli and related bacteria were associated with a notable increase in gastrointestinal infections.

These results challenge the WHO’s recent move to omit E coli from its freshwater bathing‑water guidelines, especially as public interest in wild swimming continues to surge.

Professor Paul Hunter of the University of East Anglia, the study’s lead author, noted that the 2003 guidelines he helped draft called for monitoring both E coli and enterococci in marine and freshwater environments.

He added, “The WHO’s updated guidelines now advise focusing only on enterococci, but our data show that E coli—not enterococci—is the bacterium linked to higher illness risk.”

The trial enrolled 2,368 volunteers at two river and two lake‑type sites in Hungary. Participants were randomly assigned to a 10‑minute immersion (including at least three face dips) or to a control group that stayed on shore.

Water samples were taken continuously, enabling the team to quantify each participant’s exposure to E coli, intestinal enterococci and somatic coliphages—viruses that serve as indicators of faecal pollution. Symptom surveys were conducted one week after the exposure.

Approximately 2.1% of swimmers reported gastrointestinal symptoms such as diarrhoea, vomiting, nausea, or fever, versus 1.9% of the shoreline group.

While swimming per se did not reach statistical significance for stomach illness, the risk rose sharply for those exposed to elevated E coli and coliphage levels.

Skin issues—including rashes, ulcers, or itching—were observed in 2.7% of swimmers and 1.3% of non‑swimmers, indicating that bathers faced more than double the odds of a dermatological problem.

Hunter expressed confidence that the results are relevant to the UK, noting a comparable 2006 German investigation that reached similar conclusions.

He noted, “Both Germany and Hungary produced comparable outcomes, and their climates are not dramatically different from ours, supporting broader applicability.”

Crucially, the skin complaints showed no link to the three faecal markers measured, implying that other pathogens or environmental factors may be at play.

“Recreation in fresh water does elevate the risk of skin irritation,” Hunter explained. “The exact cause remains unclear, but possibilities include cercarial dermatitis—where bird‑borne parasites penetrate the skin—and irritation from algal blooms.”

“That remains speculative,” he concluded. “What we do know is that the skin irritation is not correlated with the standard faecal pollution markers.”

Higher rates of respiratory, ear, and eye infections were observed among swimmers, yet the sample sizes were insufficient for definitive statistical analysis.

All four study sites met the EU bathing‑water standards applicable at the time, and the researchers emphasized that the randomised design yielded more robust evidence than traditional observational data.

The team cautioned, however, that the findings were derived from a single day of testing at each location and that some participants reported additional swimming outside the study sites.

Hunter concluded that the data support keeping E coli as a key indicator in freshwater monitoring and highlighted the potential of somatic coliphages for detecting unsafe conditions. “There’s a compelling case for including E coli—especially in fresh waters—within future bathing‑water standards and guidelines,” he said.

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