Tip · Cold & heat
Cold Showers (Wim Hof)
Acute cold stimulus: catecholamines rise measurably. The widely cited figures on dopamine and the immune system come from two very small studies.
Cold showering here means: at the end of your normal warm shower, turn the water to cold for 30 to 90 seconds. The tip is on this page because it is the only cold stimulus in this category that has been tested in a large randomized trial — and because the figures circulating about it come from an entirely different application.
In short
Something measurable happens. In the only large randomized trial to date, with 3,018 adults, sickness absence days fell by 29% (incidence rate ratio 0.71; p = 0.003), and 30, 60 and 90 seconds worked equally well. The number of days of illness, by contrast, did not fall: participants called in sick less often, but they were not sick less often. The cold stimulus drives noradrenaline and dopamine up sharply — measured, however, during one hour in water at 14 degrees, not under the shower. Across eleven randomized trials, the stress effect was detectable only 12 hours after the application, and an immune effect not at all.
What is behind it
The foundation is Buijze 2016: 3,018 adults between 18 and 65 years of age, with no cold-shower experience, randomized to 30, 60 or 90 seconds of hot-to-cold or normal showering, for 30 consecutive days and then for 60 days at their own discretion. 79% completed the full 30 days, and there were no serious adverse events.
The primary endpoint had two parts and was half met: sickness absence days fell by 29%, days of illness did not. The study never specified a water temperature — it was cold tap water in the Netherlands between January and March. Nothing was blinded, and both endpoints are based on self-report; with a cold shower it cannot be done any other way.
How it works
The skin cold stimulus activates the sympathetic nervous system within seconds: tachycardia, peripheral vasoconstriction, a rise in blood pressure, an involuntary gasp reflex and hyperventilation — together, the cold shock response.
The catecholamine response is the most measurable variable. During one hour of head-out immersion at 14 °C, noradrenaline rose by 530%, dopamine by 250%, metabolic rate by 350%, heart rate by 5%, systolic blood pressure by 7% and diastolic by 8%. Adrenaline remained unchanged, and cortisol showed a downward trend. The authors concluded that the changes are predominantly due to sympathetic activity, not to hormonal control loops.
Mood, stress and habituation
For mood there is a cleanly measured finding: fMRI before and after five minutes of head-out immersion showed an increase in positive affect — more active, more alert, more attentive — together with altered coupling between the default mode, frontoparietal and salience networks.
The stress effect depends on time: across eleven randomized trials, markedly reduced 12 hours after the application (SMD −1.00; 95% CI −1.40 to −0.61), but not immediately afterwards or after 1, 24 and 48 hours. And the response can be trained: three to five short immersions habituate the cold shock response, but high acute anxiety cancels this habituation again.
What is well supported
The sickness absence finding is the most robust, because it comes from the only large randomized trial and because that trial was the only one to study the shower and not the water bath: 3,018 participants, a 30-day protocol, 29% fewer sickness absence days. That all three durations worked equally well is, in practical terms, the most useful single piece of information in the entire literature — 30 seconds are enough. Also firmly measured are the catecholamines at 14 degrees, the rise in positive affect after five minutes of immersion and the habituation after three to five exposures.
What the studies show
Buijze 2016, PLOS ONE
The only large study on the shower. 3,018 people, randomized between January and March 2015 to four arms, 30 days of mandatory protocol and 60 days voluntary. Result: sickness absence days 29% lower (IRR 0.71; p = 0.003), days of illness unchanged. The authors themselves phrase it as a reduction in self-reported sickness absence.
Šrámek 2000, Eur J Appl Physiol
The source of the dopamine figure: a physiological mechanism study in young men, one hour of immersion each at 32, 20 and 14 degrees. Measurements included metabolic rate, blood pressure, diuresis, cortisol, aldosterone and the catecholamines. Only at 14 °C did noradrenaline (+530%) and dopamine (+250%) rise markedly. The paper does not define a primary endpoint in today’s sense.
Cain 2025, PLOS ONE
Eleven randomized trials, 3,177 participants, 7–15 °C, durations from 30 seconds to 2 hours, mean PEDro score 6.4. For immune function there was no significant effect either immediately (SMD −0.16) or after one hour (SMD −0.18). Inflammatory markers rose immediately (SMD 1.03) and one hour afterwards (SMD 1.26).
Zwaag 2022, Psychosomatic Medicine
48 healthy men, randomized to cold training, a breathing exercise, both or neither, followed by a challenge with 2 ng/kg endotoxin. Cold training alone did not relevantly modulate the inflammatory response (p = 0.77), the breathing exercise alone did (p = 0.002), and the combination most strongly (p = 0.02). The immunological part of the Wim Hof method depends on the breathing, not on the cold.
Where the figure comes from — and where it does not
The dopamine figure does not come from the shower but from one hour of whole-body immersion in water at 14 degrees. For 30 seconds to 3 minutes under the shower there are no comparable catecholamine measurements. The circulating participant count of eight subjects could not be verified either: the abstract speaks only of a group of young men, the full text is not freely accessible, and the review article citing it does not give a number either. The immune effect, in turn, is a sickness absence effect, not an illness effect. And the full 15-day Wim Hof program, in 42 randomized participants, changed neither heart rate, heart rate variability, blood pressure and pulse wave velocity nor affect or perceived stress. The data base is also narrow: few studies, small samples, a lack of diversity in the populations, and the mechanism studies were conducted exclusively in young healthy men.
How to do it
What was actually done in the studies: shower normally with warm water and finish with 30, 60 or 90 seconds of cold rinsing, 30 days in a row, then at your own discretion — all three durations with the same effect. The included bath studies worked with 7–15 °C and durations from 30 seconds to 2 hours, the catecholamine measurement with 1 hour at 14 °C with the head above water, the mood measurement with five minutes of immersion. Three to five short exposures are enough for habituation.
Safety
The dangerous moment is the beginning, not the duration. The cold shock response sets in within seconds and can lead to death through aspiration, hypocapnia-induced reduced cerebral blood flow and cardiac arrhythmias before core body temperature even begins to fall. Standing under the shower, the risk of drowning is practically zero, but the response itself is the same. Known or suspected arrhythmias, long QT syndrome and other channelopathies, unexplained fainting and sudden deaths at a young age in the family should be clarified with a doctor beforehand. Never lying in water or in the bathtub when you are alone: according to the WHO, around 300,000 people die from drowning worldwide every year, and the WHO explicitly names swimming alone and alcohol as risk behaviors. Acute anxiety intensifies the cold shock response instead of reducing it. Wim Hof breathing with cyclic hyperventilation and breath holding leads to hypocapnia and hypoxia and never belongs in or near water.
BK-Score Thin human evidence
| Human evidence | 4 | |
|---|---|---|
| Mechanism | 5 | |
| Safety data | 7 | |
| Hype gap | 3 | |
| Track record of use | 8 |
The much-cited tripling of dopamine comes from an investigation of a very small group of young men in 14 °C water, not from the shower. The immune data come from a Dutch study in which cold showerers called in sick less often – but were not sick less often; a meta-analysis across eleven RCTs found no immune effect at all.
The score rates the state of knowledge, not the effect. “Safety data 9” means well studied – not harmless.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)
Frequently asked questions about Cold Showers (Wim Hof)
How long do I have to shower cold for it to do anything?
In the only large randomized trial, 30, 60 and 90 seconds produced the same effect on sickness absence days. A longer duration was not better. If you are looking for a way in, you can stay at 30 seconds without giving anything away. What mattered in this study was regularity over 30 days, not the length of the individual shower.
Does my dopamine really rise by 250 percent?
This figure comes from a single investigation in which young men sat up to their necks in water at 14 degrees for a full hour. It was not measured in the shower and not at 30 seconds. For the cold stimulus under the shower there are no comparable catecholamine measurements.
Will it make me get sick less often?
The participants in the large Dutch study called in sick 29 percent less often, but were not sick less often: the number of days of illness did not differ. A meta-analysis of eleven randomized trials found no significant effect on immune function at all. The finding is real, but it concerns behavior, not infection.
Is cold showering dangerous?
The cold shock response is the same for everyone: gasp reflex, hyperventilation, rise in blood pressure and heart rate within seconds. Standing under the shower, this is unproblematic for people with a healthy heart; lying in water, it can end fatally. If you have known arrhythmias, unexplained fainting or sudden deaths in the family, you should have this clarified by a doctor beforehand.
Is Wim Hof breathing part of it?
In the study that tested the components of the method separately, the anti-inflammatory effect came from the breathing exercise, not from cold training. Cold alone did not relevantly change the inflammatory response. However, the breathing with hyperventilation and breath holding must never be practiced in or near water, because it can lead to loss of consciousness.
Will I get used to it?
Yes, and quickly: three to five short cold-water exposures are enough to markedly weaken the cold shock response. Strong fear of the stimulus can, however, prevent or reverse this habituation. A gradual start therefore achieves more than forcing yourself through with gritted teeth.
Related
- In depthSauna & cold (hormesis)
- Same category: Cold & heatIce bath
- Same category: Cold & heatSauna 20 min, 4× per week
- Shared topicForest bathing (shinrin-yoku)
- Shared topicButeyko breathing for allergy and asthma sufferers
- Shared topicBox Breathing (4-4-4-4)
Sources
Open in the database – with all tips, filters and BK-Score (German app)
Information only, not medical advice and not a usage recommendation. If you have pre-existing conditions and before major changes, consult a doctor. Last updated: 2026-10-06.