People who took cold showers regularly reported 31% fewer days off work because of illness than people who did not, according to a pooled analysis of three randomized controlled trials involving 719 participants. The work comes from psychologist Lena Glaser at the University of Basel in Switzerland and has not been peer-reviewed. Compared with people who mostly showered warm, the cold-shower group reported 26% fewer illness days.
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Glaser carried out the research as part of her doctoral dissertation, which examined the psychological factors involved in adopting a new behavior.
Three trials, 719 participants and a self-reported outcome
The analysis combined three trials in which people were asked to take cold showers, and counted what they reported afterward. The 31% figure refers to days off work, the measure the researchers call sickness absence, and it sits alongside the 26% reduction in illness days. ScienceAlert’s coverage says the authors wrote that the pooled results showed a clear reduction in both illness days and sickness absence.
The data are self-reported. Nobody checked employer records or clinic visits, so the numbers reflect what participants said about their own health and work.
A second limit matters more for interpretation. In the pooled analysis, participants were grouped by how often they actually took cold showers, not by random assignment, so the comparison is less clean than the trial designs it draws on. The paper is a preprint submitted to the Journal of Health Psychology and hosted in the University of Basel repository, and ScienceAlert’s quotes come from that manuscript.
Grouping by habit raises a selection problem. People who keep taking cold showers for weeks may differ from those who quit, perhaps in motivation, health or routine, and those differences could shape sick-day reports independently of the water temperature. The 31% figure, the 26% comparison with mostly warm-shower takers and the 29% from the 2016 trial point in the same direction, yet none of the three settles the matter.
Peer review will test several details the preprint cannot settle alone: how sickness absence was defined across the three trials, whether the pooling plan was fixed in advance, and how participants who dropped out were counted. Each choice can move a percentage like 31% by a noticeable margin in a sample of 719.
Dropouts early, adherence later
Many participants quit within the first two weeks, but attrition slowed after that. Among those who stuck with the habit at least 70% of the time, between 77.3% and 90% reported taking a cold shower in any given week, depending on the trial. Glaser said that pattern suggests people gradually get used to it.
The authors also reported that well-being improved, which they said directly refutes the common initial concern that a cold shower would feel unpleasant enough to hurt mood. Psychological well-being rose slightly on questionnaires. Physical well-being also rose but not by a statistically significant amount, so the clearest signal remains the absence figure rather than any broader health claim.
The well-being findings matter for a practical reason. Reluctance is the main reason people avoid cold showers, and the Basel analysis found no sign that the habit made people feel worse. For a behavior that costs nothing and needs no equipment, the combination of mild mood gains and lower reported absence is why the preprint drew attention, even though the evidence is not yet strong enough to prescribe it.
Earlier research and a possible immune explanation
The new analysis was not designed to test a mechanism. A 2024 study in the Journal of Thermal Biology found increased signs of an immune response in people who took cold showers, and cold water immersion research has reported similar effects, as in an older immersion paper. ScienceAlert suggests immune changes could explain fewer sick days, while stressing that more research is needed.
An earlier randomized trial published in PLOS ONE in 2016 found a 29% reduction in work absence due to illness, but no reduction in the number of days when people felt ill. That split bears on the new result: a cold shower habit may change whether someone calls in sick without changing how often they feel unwell.
Advice from the Basel researchers
Glaser advised starting slowly, lowering the temperature in stages and adjusting to stay comfortable. The water does not have to be equally cold every day, she said, and it is important to listen to the body and pay attention to how it feels. The University of Basel has a news page on the work that frames cold showers as saving water, energy and money as well as possibly aiding health.
Whether peer review leaves the 31% figure intact is the open question. Until the Journal of Health Psychology decides on the manuscript, the number rests on self-reports from 719 people grouped by habit, and Glaser’s dissertation, also posted by the university, is the only fuller account available to readers now.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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