You have probably seen the videos. Someone steps into icy water, lets out a few deep breaths and climbs out looking transformed. The claims that follow range from faster metabolism to better moods.
A large Dutch trial of 3,018 adults, published in PLOS ONE in 2016, found something striking. People who finished their shower with 30 to 90 seconds of cold water took 29% fewer sick days off work over the next 90 days.
It is the single strongest piece of evidence behind the whole cold-exposure trend. But the study also found something the headlines rarely mention. People in the cold-shower groups reported just as many days feeling ill as the control group. They simply took less time off work.
A broader look at the picture lands softer. A 2025 systematic review in PLOS ONE pooled 11 randomized trials with 3,177 participants and found no consistent sign that cold exposure improves mood or delivers meaningful immune benefits.
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What the evidence may support
The 2025 review did point to a few areas where cold water seems to do something. Stress levels dropped, but only around 12 hours after a cold plunge, not immediately. Men reported better sleep after ice baths. Women did not.
A separate 2024 trial in the Journal of Thermal Biology followed 60 healthy adults for 90 days. Daily cold showers raised certain antibody levels and a signaling molecule called IL-2, which helps immune cells multiply.
The researchers framed it as a modest shift in the immune system, not a full overhaul. The trial was small, and the finding has not yet been replicated in larger studies.
Cold-water immersion also has some track record in sports recovery. A Cochrane review found reduced muscle soreness in the days after hard exercise compared with passive rest, though the ideal temperature and length of exposure remain unclear.
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What the big claims get wrong
The bigger promises have thinner backing. According to Harvard Health, popular claims about fat burning, speeding up metabolism and lifting depression are not supported by current research.
The 2025 PLOS ONE review reached a similar conclusion on mood. There was no consistent benefit across the trials. The same review also flagged a less flattering finding. Cold water triggered a short-term inflammatory spike right after immersion and one hour later.
Who should think twice before trying it
Harvard Health lists groups who should talk to a doctor before taking the plunge. People with heart disease, high blood pressure, diabetes or circulation problems may face real risks from sudden cold exposure.
For most healthy adults, a short cold shower appears safe. But the current evidence does not back it as a stand-in for sleep, regular exercise or a balanced diet.
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This article is made and published by Mie Hermansen, who may have used AI in the preparation.