Plate Nº 86 · recorded November 11, 2026
Health & Medicine ResearchReported finding
Swimmers in Freshwater Study Twice as Likely to Get Rashes, Skin Problems
A randomized trial of 2,368 volunteers found freshwater swimmers were more than twice as likely to report rashes, with stomach illness risk rising 73% per tenfold jump in E. coli.
By James Calloway3 min read630 words
In brief
- 2,368 volunteers were randomized to swim for ten minutes or stay on shore at four Hungarian freshwater sites.
- Swimmers were more than twice as likely to report skin complaints such as rashes and itching.
- Each tenfold rise in E. coli concentration carried an approximately 73% increase in stomach illness risk.
- Just over 2% of participants developed gastrointestinal symptoms; a similar share reported skin problems.
- The study appears in the International Journal of Hygiene and Environmental Health.
Swimmers who dunked their heads in rivers and lakes were more than twice as likely to report skin complaints — rashes, itching — than people who stayed dry on shore. That's the headline finding from a randomized trial of 2,368 volunteers at four freshwater bathing sites in Hungary, run by researchers at the University of East Anglia and published in the International Journal of Hygiene and Environmental Health.
The trial design matters here, because most water-quality studies watch people who chose to swim. This one didn't. Participants were randomly assigned either to swim for ten minutes or to remain on shore. The swimmers were told to put their heads underwater at least three times. Random assignment lets the researchers compare like with like, and that comparison produced uncomfortable numbers.
How strong is the illness link?
The clearest signal involved E. coli, a bacterium that lives in the gut and serves as the standard yardstick for fecal contamination in water. Each tenfold increase in E. coli concentration came with roughly a 73% increase in the risk of stomach illness. Higher levels of certain viruses that infect gut bacteria tracked with illness too.
The researchers also found something the standard toolkit misses: skin problems did not always follow the fecal-contamination measurements. Rashes and itching may have other causes, including naturally occurring parasites linked to "swimmer's itch." So the bugs that upset your stomach and the ones that upset your skin don't necessarily arrive together, and current water-quality indicators may not capture both.
That's a real gap. Water can meet established quality standards and still make people sick — which is, in effect, what this study demonstrated at sites that presumably passed inspection.
What does this change for swimmers?
Not much yet, honestly. The absolute numbers are reassuring. Just over 2% of participants developed gastrointestinal symptoms, and a similar proportion reported skin problems. Eye, ear and respiratory infections were uncommon. Most illnesses were mild and short-lived.
The study also can't tell you whether your particular swimming spot is safe on any given day. Water quality shifts with rainfall, runoff, pollution and other local conditions, and a single trial at four Hungarian sites doesn't generalize to every riverbank in every country. The authors themselves stress the need for careful follow-up research and independent confirmation before these results can guide routine healthcare decisions.
Still, the practical takeaway is hard to argue with. Clear-looking water is not clean water. Microbes are invisible, and visual appearance alone is not a reliable guide to safety — especially after rain or anything else that might wash contamination in. Check public monitoring data and local warnings before you swim; those remain the best tools available.
Why this matters now
Open-water swimming has grown markedly more popular, and rivers and lakes offer genuine exercise and enjoyment. Nobody in this study is telling people to stop. The research does not suggest that everyone should avoid freshwater swimming. What it supports is better monitoring and clearer public information, so swimmers can make informed choices about where and when to get in.
There's also a scientific question underneath the public-health one. If E. coli and gut-infecting viruses both correlate with illness, but skin complaints don't track with either, then regulators may be measuring the wrong things, or not enough of the right ones. These markers, the researchers suggest, may help scientists work out which measurements best reflect the actual health risks of freshwater swimming. That's a promise of better indicators — with the caveat that this is one trial, preliminary, awaiting replication.
So: keep swimming if you enjoy it. Keep your mouth shut underwater if you can. And don't trust your eyes when it comes to water quality.
via knowridge.com (Source)
More from James Calloway
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Staff writer covering regulation, policy and their impact on general science news at SciBeat.
346 articles
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