therapies · education ·
3,018 People Took Cold Showers For A Month. Sick Days Fell 29%, Sick Feelings Didn't
The largest cold shower trial ever run split one outcome cleanly in two. People took fewer days off work. They did not report fewer days feeling ill.
Most cold exposure research is small. Twenty people in a lab, a handful of measurements, a cautious conclusion.
Then there is this one: 3,018 adults, randomized, with an outcome nobody can argue about because it came off employment records rather than a questionnaire.
And the result splits in a way that is far more interesting than the headline version.
What they did
Adults aged 18 to 65, without severe comorbidity and with no routine experience of cold showering, were randomized one-to-one-to-one-to-one into four groups (Buijze et al., PLOS One, 2016).
Three groups finished their normal warm shower with cold water, for 30, 60 or 90 seconds, every day for 30 consecutive days. The fourth group carried on as normal. After the 30 days, the intervention groups could keep going at their own discretion for another 60.
79% of the intervention participants completed the full 30-day protocol, which for a daily cold shower is a better adherence rate than most supplement trials manage with a pill.
The result, in two halves
Sickness absence from work fell 29% in the cold shower groups against control, with an incident rate ratio of 0.71 (P = 0.003).
Illness days showed no significant group effect.
Read those together, because the trial is far more useful that way than either sentence alone.
People took fewer days off work. People did not report fewer days feeling unwell.
A routine (hot-to-) cold shower resulted in a statistical reduction of self-reported sickness absence but not illness days in adults without severe comorbidity.
Buijze et al., PLOS One, 2016
That is the authors’ own conclusion, and notice they put both halves in one sentence rather than leading with the good one.
What that split probably means
We do not know, and we would rather say so than invent a mechanism.
But the plainest reading is worth stating: people got ill about as often and went to work anyway. Not because the cold killed a virus, but because it changed something about their threshold for calling in.
That is not a small thing, and it is not nothing. Feeling able to get on with your day when you are a bit under the weather is a real quality of life. It is also completely different from an immune effect, and the two get blurred constantly in how this trial is quoted.
Anyone citing this study as proof that cold showers boost immunity is quoting half of it.
One more honest limit. Sickness absence here was self-reported, and the trial was not blinded, which it could not be. People who signed up for a cold shower study and stuck with it for thirty days knew what they were doing, and knowing you are doing something rigorous for your health can move a decision about whether to go to work.
The paper that is not evidence
You will meet a 2008 article proposing that adapted cold showers could treat depression. It gets cited constantly, usually with the word “study” attached to it.
It was published in Medical Hypotheses, a journal whose entire purpose is to publish ideas for consideration rather than results. It is a proposal. There is no trial in it, no control group and no outcome data (Shevchuk, Medical Hypotheses, 2008).
We are naming it only so you can recognise it when it is handed to you as proof. A hypothesis is where research starts, not what it concludes.
For what cold immersion does to mood on actual measurement, the work worth knowing used functional MRI after a five minute cold-water immersion and found increased positive affect, people reporting feeling more active, alert, attentive, proud and inspired, alongside reductions in distress and nervousness (Yankouskaya et al., Biology, 2023). That is a measured mood change from whole-body immersion, which is a much larger stimulus than a cold finish to a warm shower, and we cover it in do cold plunges actually work.
What we are and are not saying
| Claim | Our line |
|---|---|
| Cold showers treat, cure or prevent illness | Never |
| Sickness absence fell 29% in a randomized trial | Yes, 3,018 people, IRR 0.71, P = 0.003 |
| Self-reported illness days fell | No. No significant group effect |
| Cold showers boost immunity | Unsupported. People missed less work, not less illness |
| Longer cold is better | Untested here. 30, 60 and 90 seconds were pooled for the headline |
| Cold showers treat depression | No. That paper is a hypothesis, not a trial |
| It is low risk | For most people, yes. No related serious adverse events were reported |
Where the design shows up
The thing that survived in this trial was not a marker. It was a decision.
Three thousand people did something mildly unpleasant on purpose, every morning, for a month, and what changed was how willing they were to show up. No blood test was needed to detect it, because it showed up in whether somebody got in the car.
There is a version of that in a lot of what we write about. The body responds to being asked, and a small hard thing done daily seems to move the threshold for what counts as too hard. The cold is not really the intervention. The deciding is.
“The plans of the diligent certainly lead to advantage, but everyone who is hasty certainly comes to poverty.” Proverbs 21:5, NASB
The verse carries the conviction. Three thousand and eighteen people carry the number.
What to do this week
If you want to try it, the tested version is the easy one.
Take your normal warm shower. Finish it cold for 30 seconds. Thirty seconds is a real arm of a real trial, and it did as well as ninety in the pooled result. There is nothing in this literature saying you need to suffer more than that.
Do it daily for a month before deciding anything, since that is the exposure that was studied.
And be clear with yourself about what you are buying. On this evidence it is not fewer infections. It is, maybe, a slightly higher tolerance for showing up on a day you would rather not.
Read this next: what whole-body cold immersion does, which is a much bigger stimulus than a cold finish: do cold plunges actually work. The cost of plunging at the wrong moment: plunging after you lift. And the metabolic side of cold: cold really does switch on brown fat.
Sources
- Buijze GA, Sierevelt IN, van der Heijden BC, Dijkgraaf MG, Frings-Dresen MH. “The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial.” PLOS One, 2016;11(9):e0161749. https://pubmed.ncbi.nlm.nih.gov/27631616/
- Yankouskaya A, Williamson R, Stacey C, Totman JJ, Massey H. “Short-Term Head-Out Whole-Body Cold-Water Immersion Facilitates Positive Affect and Increases Interaction between Large-Scale Brain Networks.” Biology, 2023;12(2):211. https://pubmed.ncbi.nlm.nih.gov/36829490/
- Shevchuk NA. “Adapted cold shower as a potential treatment for depression.” Medical Hypotheses, 2008;70(5):995-1001. https://pubmed.ncbi.nlm.nih.gov/17993252/
Article metadata retrieved from PubMed. Photograph from Pexels. Scripture quoted from the New American Standard Bible.
Educational content from True Health Solutions. We do not diagnose or prescribe, and nothing here is a substitute for care from someone who knows your history. The body heals. We write about what supports that design.
Questions people ask
- Do cold showers actually do anything?
- In a randomized trial of 3,018 adults, 30 days of ending a shower cold produced a 29% reduction in sickness absence from work compared with a control group. For self-reported illness days there was no significant difference. Both results come from the same trial.
- How long do you have to stand in it?
- The trial randomized people to 30, 60 or 90 seconds of cold at the end of a normal hot shower. All three intervention arms were pooled against control for the headline result, and 79% of people completed the 30-day protocol.
- How can sick days fall if illness days did not?
- That is the honest puzzle of this trial and we are not going to paper over it. One plain reading is that people got ill just as often and went to work anyway. Feeling more able to push through is a real effect, and it is not the same as being less sick.
- Was it safe?
- No related serious adverse events were reported in the trial. The usual cautions about cold and the heart still apply to whole-body immersion, which is a different and more demanding thing than a cold finish to a warm shower.
- Does it treat depression?
- No trial shows that. The paper people cite for it is a 2008 article in Medical Hypotheses, which is a journal for proposing ideas, not testing them. It is a hypothesis, and citing it as evidence is the single most common error in this topic.
