How does the Cold Shower Challenge boost mental and physical health?

In eight years of doing other people’s faces, the single most repeated sentence I have heard in the chair is that cold water closes your pores. It does not. That sentence is also the reason I went looking properly at the cold shower challenge, because if the beauty claim attached to it is that shaky, I wanted to know what the rest of it rests on.

Start with the claim I hear most, because it is the wrong one

Pores do not open and close. They have no muscular ring around them and no mechanism for it, which is why dermatologists spend a good part of their lives correcting this. What cold water does is constrict the small blood vessels near the surface, which makes skin look momentarily tighter and less flushed. Take a photograph an hour later and the effect has gone.

That is not nothing for my purposes. A cold rinse before a shoot genuinely helps with morning puffiness around the eyes, and I use it. I describe it as a temporary appearance change, which is what it is, rather than pretending I have altered someone’s skin. The same applies to the hair claim: a cold rinse can leave hair looking glossier by flattening the cuticle briefly, and it is a styling trick, not a substitute for how you actually treat your hair.

The one large trial worth knowing about

It is Buijze and colleagues, published in PLOS ONE in 2016, and it is unusually well designed for this field. They randomised 3,018 adults in the Netherlands to finish their normal warm shower with 30, 60 or 90 seconds of cold water, or to carry on as usual, every day for 30 days.

The cold shower groups reported 29 per cent less sickness absence from work than the control group. Read the small print, though: the number of days people reported actually feeling ill did not differ between groups. People took cold showers and went to work anyway. The duration made no difference either, so 30 seconds performed as well as 90. Everything was self-reported, which is the study’s main weakness.

What a 2025 review of the whole field concluded

That the picture is thinner and stranger than the enthusiasm suggests. A systematic review and meta-analysis of cold-water immersion published in PLOS ONE in January 2025 pooled 11 randomised trials covering 3,177 participants, and found something genuinely odd about timing.

The authors are blunt about the state of the evidence: few trials, small samples, and study populations that all look rather similar to each other. Both these papers are indexed on PubMed and turn up in Google Scholar if you want to read them yourself rather than take a summary’s word for it, mine included.

The Wim Hof research tested a bundle, not a shower

This distinction gets lost constantly. Wim Hof, the Dutch athlete known as the Iceman, teaches a method combining cold exposure, cyclic hyperventilation with breath holds, and meditation. In 2014, Kox and colleagues published a study in PNAS in which 12 people trained in the method and 12 untrained controls were injected with a bacterial toxin. The trained group released more adrenaline, showed a blunted inflammatory response and reported fewer flu-like symptoms.

It is a striking result, and later work suggests the breathing, not the cold, does most of that particular lifting. Twelve people is also twelve people. Citing it to justify a cold morning shower is a stretch that the researchers themselves never made.

Where the depression claim actually comes from

It comes from a hypothesis paper, not a trial. The commonly quoted source is Nikolai Shevchuk’s 2008 article in Medical Hypotheses, a journal whose remit is publishing untested ideas. Shevchuk proposed that brief cold exposure might act on mood through cold receptors in the skin, and the informal testing he described involved a handful of people, none with a clinical depression diagnosis.

It remains an interesting idea that nobody has properly tested at scale. Presenting it as evidence that cold showers treat depression, which happens constantly online, is not something the paper supports.

Who should be careful, and it is not a short list

Sudden cold on the skin triggers the cold shock response: an involuntary gasp, uncontrolled fast breathing and a jump in heart rate, all in the first minute. In a shower that is unpleasant. In open water it is the reason people drown, which is why a cold shower habit and a dip in a lake are not the same activity and should never be treated as one.

Talk to your GP first if you have a heart condition or high blood pressure, Raynaud’s phenomenon, epilepsy, asthma triggered by cold air, or if you are pregnant. If you feel faint, get chest pain, or cannot control your breathing, get out and get warm. That is not you failing the challenge.

How I would run the 30 days if I were starting tomorrow

1. Shower normally and warm. The cold goes at the end, not the beginning.
2. Start at 15 seconds. The trial found 30 seconds worked as well as 90, so there is no prize for endurance.
3. Breathe out slowly as the water turns. Fighting the gasp is what makes the first ten seconds horrible.
4. Keep it off your head and face at first if you find that overwhelming, then work up.
5. Write down one line a day about sleep and energy. Thirty days of your own notes will tell you more about whether this suits you than any study of 3,000 strangers.

My own honest report, after doing it through a Liverpool winter: I did not get ill less often, and I am not convinced it made me calmer. I did wake up properly, which on a 5am call time is worth the thirty seconds on its own.

This is general information and not medical advice. Cold water exposure carries real cardiovascular risk for some people, and cold showers are not a treatment for depression or anxiety. Speak to your GP before starting if you have any health condition, and seek help for low mood rather than showering through it.

Sources: Buijze GA et al., The effect of cold showering on health and work: a randomized controlled trial, PLOS ONE, 2016; systematic review and meta-analysis of cold-water immersion on health and wellbeing, PLOS ONE, January 2025; Kox M et al., PNAS 111, 2014; Shevchuk NA, Adapted cold shower as a potential treatment for depression, Medical Hypotheses 70(5), 2008; RNLI guidance on cold water shock.