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Only 37% in Trials Stuck With Daily Cold Showers
In A Nutshell
- Swiss adults who took mostly cold showers for 12 weeks reported 26% fewer sick days and 31% fewer days off work.
- Groups were sorted by actual shower habits, not random assignment, so the results show a link, not proof.
- Only 37% stuck with daily cold showers for all 12 weeks, and quitting was most likely in the first few weeks.
- Cold showers also avoided an estimated 8.8 metric tons of carbon dioxide across 586 participants.
Cranking the shower to cold every day sounds like a dare, not a health plan. Yet in a set of Swiss trials, people who took mostly cold showers over 12 weeks reported 26% fewer sick days and 31% fewer days off work than people who took cold showers less often. One catch: the comparison was built on what people really did in the shower, not on which group they were assigned to, so the results show a link, but they do not prove that cold water protects health.
Lena Glaser, a psychology researcher at the University of Basel, combined three trials in her doctoral dissertation. The health results come from a manuscript submitted to the Journal of Health Psychology, and the dissertation does not say whether other scientists have reviewed it yet.
Sick days were only part of Glaser’s goal. She used cold showers as a test case for a stubborn climate problem: getting people to keep up habits that help the planet but feel miserable. Heating water accounts for roughly 15% to 25% of home energy use in wealthy countries, according to the dissertation, and a cold shower skips that cost entirely.
Regular Cold Showers Tied to Fewer Sick Days in Swiss Trials
Three experiments ran in Switzerland between 2019 and 2024, with adults recruited through ads, social media and word of mouth. The final analysis covered 735 of them, and 719 of those had complete health data. Ages averaged about 26, and roughly two-thirds were women. People with conditions that cold water can make worse, such as severe heart disease or severe asthma, were left out.
Cold shower groups were told to turn the water to its coldest setting every day, for anywhere from 30 seconds to several minutes depending on the trial. Only one trial, with 166 people, assigned a group to keep showering as usual. The other two tested ways to help people stick with cold showers, so their warm group is mostly people who dropped the habit or never fully took it up. At the start and then monthly, participants reported online how many days they felt sick and how many they missed work.
Researchers then sorted people by what they actually did. Anyone who took cold showers at least 70% of the time counted as a cold shower user: 459 people, or 62.4% of the 735. The other 276 formed the warm group, though some of them took cold showers part of the time. People who stick with cold water may be tougher or healthier, which could explain part of the gap.
In everyday terms, that gap is small. Participants averaged about three sick days in the month before the trials began, so a 26% drop likely amounts to a day a month or less. Cold shower users also reported a small boost in well-being on a standard five-question survey, while physical well-being and skin health showed no clear difference.
One more caution: sick days and missed work came from participants’ memories, not medical records, and everyone knew which group they were in. Trial by trial, the drop in sick days was clear in only the largest of the three, and the drop in missed work in only one of the smaller two.
Quitting Cold Showers Is Most Likely in the First Few Weeks
A second analysis followed who quit and when, using two of the trials with 586 participants. Researchers counted someone as quitting after a full week with no cold showers. Only 37% stuck with daily cold showers for all 12 weeks. Quitting was most likely in the first few weeks, and women quit at a higher rate than men, with about a third more risk.
Four short mindset videos in one trial did no better than the comparison group. In the other trial, weekly video training meant to build confidence backfired: that group quit sooner, and only 14% took cold showers at least 70% of the time, compared with 47% of that trial’s comparison group.
Cold Showers Cut an Estimated 8.8 Metric Tons of Carbon Dioxide
Based on those same 586 participants’ own reports, the dissertation estimates that about 27,664 cold showers were taken, avoiding 8.8 metric tons of carbon dioxide from water heating, roughly what a car emits over 36,000 miles of driving. It rests on assumptions about shower length and water heating, not readings from household energy meters.
Another, untested part of the dissertation asks whether motivational interviewing, a counseling style used in addiction treatment that helps people talk themselves into change, could help with unpleasant but climate-friendly habits.
A payoff people can feel, even a small one, may sell a tough habit better than guilt does. Whether cold water deserves a spot in the health plan still needs a trial that assigns people to cold or warm showers and checks illness against medical records.
Disclaimer: This article summarizes research findings for general information and is not medical advice. The research reported a link between cold showering and fewer sick days, not proven cause and effect, and cold water exposure is not safe for everyone. Anyone with a heart condition, asthma, circulation problems, or other health concerns should talk with a doctor before trying it.
Paper Notes
Limitations
Sick days and sick leave were self-reported, which leaves room for memory errors and answers shaped by what looks good, and there was no medical confirmation of illness. The main health comparison grouped participants by actual showering behavior (at least 70% cold showers), not by random assignment, so the 26% and 31% differences may partly reflect traits of people who kept up the habit. Only one trial (166 people) assigned a warm-shower control group; in the other two, the warm group consisted mainly of participants who did not reach the 70% threshold, even though the dissertation’s summary describes the comparison groups as continuing usual showering. The two groups differed at baseline in gender (women made up 65% of the cold shower group and 75% of the warm group) and in which study they came from. One of the three trials, which enrolled 309 people, lost 46% of them from the analysis because self-reported participant IDs did not match across surveys, which the authors note could skew results. Only people with usable data are counted in the 735, and that trial was also smaller than planned. The trials were unblinded (participants knew their group), and, when each trial was analyzed alone, the drop in sick days was statistically clear in only one trial (the largest) and the drop in missed work in only one other. Samples were largely healthy young adults willing to try an uncomfortable habit, and people with conditions that cold exposure can worsen were excluded, so results may not apply to everyone. The dissertation’s summary mentions improved vitality, but its results table shows no significant gain in physical well-being, so only the significant well-being result is reported here. The carbon estimate rests on calculated averages and assumptions, not household energy measurements, and the dissertation lists moral licensing (people offsetting savings with other consumption) as unexamined. The motivational interviewing work is conceptual and was not tested against other approaches.
Funding and Disclosures
According to the adherence manuscript, the research received no external funding and was carried out with institutional funds from the University of Basel, and the authors declare no competing interests. The dissertation also discloses that Google’s Gemini was used for language refinement across the work.
Publication Details
This article is based on the doctoral dissertation “Breaking the Habit: Psychological Strategies to Promote Health and Sustainability” by Lena Glaser, submitted to the Faculty of Psychology at the University of Basel (Basel, 2026) and supervised by Prof. Dr. Jens Gaab and Prof. Dr. Ulf Hahnel. It includes three manuscripts. Study II, “The Influence of Cold Showering Interventions on Well-being and Health-Related Outcomes: A Series of Three Randomized Controlled Trials” by Glaser, L., Zehner, T., & Gaab, J., was submitted to the Journal of Health Psychology. Study III, “Strategies to Promote Cold Shower Adherence: A Survival Analysis Comparing Mindset and Self-Efficacy Training in Two Randomized Controlled Trials” by Glaser, L., Zehner, T., & Gaab, J., was submitted to PLOS ONE. Study I, “Motivierende Gesprächsführung im Dienst der Nachhaltigkeit” by Glaser, L., Schmid, O., & Gaab, J., is listed as accepted for publication in the journal PERSON. Peer review outcomes for the submitted manuscripts are not established in the dissertation. DOI: none listed in the dissertation. The full text is open access through the University of Basel’s repository, edoc.unibas.ch.
