People who swim in rivers and lakes face more than twice the risk of developing skin rashes and irritation compared to those who stay on shore, according to the largest controlled study of wild water bathing to date. The research, published by The Guardian, examined health outcomes among thousands of bathers at freshwater sites in Hungary.
Scientists also found that while swimming itself did not automatically increase intestinal illness rates, bathers exposed to water with high levels of Escherichia coli and coliphage viruses experienced a sharp rise in stomach disorders. The findings have prompted calls for health authorities to reconsider international freshwater safety standards.
Wild water swimming has surged in popularity across Europe in recent years, driving public concern over river pollution and sewage discharges. In response, environmental agencies and public health bodies monitor microbiological markers to determine whether designated bathing waters are safe for human contact.
Controlled experiment in Hungary
The controlled study involved 2,368 participants at four bathing locations in Hungary, comprising two river sites and two lake sites. All four locations met the European Union water quality standards for bathing that were in force at the time of the trials.
Researchers randomly divided the volunteers into two groups to test the health impacts of freshwater exposure. One group spent 10 minutes in the water and submerged their faces at least three times, while the control group remained on the shore without entering the water.
Throughout the experiment, scientists took regular water samples to measure levels of E. coli, intestinal enterococci, and somatic coliphages. Somatic coliphages are viruses that infect bacteria and serve as a key indicator of fecal contamination in water bodies.
One week after the trials, researchers surveyed participants about their health. Among those who swam, 2.1 percent reported gastrointestinal symptoms, including diarrhea, vomiting, or nausea accompanied by a fever. By comparison, 1.9 percent of participants who stayed on the bank reported similar stomach issues.
Surprise findings on skin irritation
The most unexpected outcome of the study was the sharp disparity in skin problems between bathers and non-bathers. Rashes, sores, or itching were recorded in 2.7 percent of swimmers, compared to just 1.3 percent of participants who stayed out of the water.
Despite the double risk, researchers were unable to link the skin conditions to any of the three tested markers of fecal pollution. Paul Hunter, a professor of medicine at the University of East Anglia who led the study, said people entering fresh water face a genuinely higher risk of skin irritation, though researchers do not yet know the exact cause.
The University of East Anglia is a public research university located in Norwich, England, known for its work in medicine and environmental sciences. Hunter suggested potential explanations could include cercarial dermatitis, commonly known as swimmer's itch, which is an allergic skin reaction caused by bird parasites that can penetrate human skin. He added that irritation from freshwater algae in rivers and lakes could also be a factor.
Hunter emphasized that these potential causes remain unproven hypotheses. The only definitive finding regarding skin irritation is that it does not correlate with standard indicators of fecal contamination.
Challenging WHO freshwater guidelines
The study's conclusions directly challenge updated freshwater guidance from the World Health Organization, the specialized United Nations agency responsible for international public health. Hunter, who previously served on the panel that drafted earlier WHO recommendations, noted that past guidance advised monitoring both E. coli and enterococci in marine and fresh waters.
However, newer WHO guidelines shifted focus almost exclusively to enterococci. Hunter acknowledged it was somewhat awkward to admit, but the research showed enterococci were not associated with an increased risk of illness, whereas E. coli was strongly linked to stomach trouble.
Based on the trial evidence, Hunter advocated for restoring E. coli as a core safety metric in freshwater quality testing. He also recommended introducing somatic coliphage testing as an additional indicator of waterborne health hazards.
Relevance to Britain and study limits
Although the trial took place in Hungary, Hunter stated that the findings are fully applicable to the United Kingdom. He noted that German researchers previously obtained similar results, demonstrating a consistent pattern across multiple European countries.
Scientists noted several limitations in the trial design. Testing took place over just a single day at each of the four locations, and some participants reported swimming at other water sites during the one-week follow-up period.
Researchers also recorded higher instances of respiratory, ear, and eye infections among swimmers. However, the total number of infected cases was too small to establish statistically reliable conclusions.
Additional expert health advice
Separately, health experts referenced in the report cautioned consumers against eating damaged or discolored salad greens. Scientists warned that when salad leaves display a rusty or brown tint rather than a pale, clean appearance, it signals that the produce has begun to spoil.
Upon being cut, plants initiate a natural defense mechanism by activating the enzyme phenylalanine ammonia-lyase, causing phenolic compounds to accumulate at damaged sites. When exposed to air, these compounds oxidize and turn brown in a process similar to a sliced apple, rendering the food potentially hazardous for human consumption.
