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One cold-shower trial supplied 3,018 of the 3,177 people in a meta-analysis of cold water and health

The 2025 PLOS ONE review pooled 11 randomized studies of cold showers and baths and reported effects on stress, inflammation, sleep and quality of life. Several of those findings come from one study apiece.

The paper

Effects of cold-water immersion on health and wellbeing: A systematic review and meta-analysis

Cain T, Brinsley J, Bennett H, Nelson M, et al.. PLOS ONE, 2025;20(1):e0317615.

Read the paper ↗PubMed 39879231 ↗Free full text ↗

See the study at a glance

Design
Systematic review and meta-analysis
People
11 studies, 3,177 people
Who they were
Participants were 55.4% female, and every woman came from the Dutch cold-shower trial. The other ten studies enrolled 7 to 26 men each.
What they did
The studies used cold showers or baths at 7–15°C for between 30 seconds and two hours, and immersions reached the chest or higher. The review pooled each cold group's change from before to after exposure.
How long
From the moment of immersion to 48 hours later, plus one 90-day trial

These numbers came out of it

3,018

Of the review's 3,177 participants, 3,018 came from one cold-shower trial.

+1.03

Inflammatory markers rose by a standardized 1.03 right after immersion, and both studies behind that number had men do resistance exercise first.

−1.00

Stress measures fell by a standardized 1.00 at 12 hours, and every data point came from one Lithuanian lab.

±0.09

The paper's text prints the immediate stress estimate as −0.09, and its forest plot shows +0.09.

The researchers did this

The review searched for randomized trials of cold-water immersion and health and found 11, with 3,177 participants.Source 1 · Meta-analysisEffects of cold-water immersion on health and wellbeing: A systematic review and meta-analysisCain T, Brinsley J, Bennett H, et al.. PLOS ONE, 2025.Read the paper ↗PubMed ↗ The Dutch cold-shower trial supplied 3,018 of them and every one of the women.Source 2 · Randomized trialThe Effect of Cold Showering on Health and Work: A Randomized Controlled TrialBuijze GA, Sierevelt IN, van der Heijden BCJM, et al.. PLOS ONE, 2016.Read the paper ↗PubMed ↗ The other ten studies each enrolled 7 to 26 men. Exposures ran from 30-second showers to two-hour immersions at 7–15°C.

The analysis pooled each cold group's change from before to after exposure. By that measure, inflammatory markers rose immediately (standardized mean difference 1.03) and an hour later (1.26).Source 1 · Meta-analysisEffects of cold-water immersion on health and wellbeing: A systematic review and meta-analysisCain T, Brinsley J, Bennett H, et al.. PLOS ONE, 2025.Read the paper ↗PubMed ↗ Both estimates come from two studies in which men got into cold water after resistance exercise. In one of them, men who rested after squats had a bigger rise in the inflammatory signal IL-6 at 30 minutes than men who took the cold bath.Source 3 · Crossover trialCold-water immersion blunts and delays increases in circulating testosterone and cytokines post-resistance exerciseEarp JE, Hatfield DL, Sherman A, et al.. European Journal of Applied Physiology, 2019.Read the paper ↗PubMed ↗

Stress fell 12 hours after immersion (−1.00) and showed no effect at 0, 1, 24 or 48 hours.Source 1 · Meta-analysisEffects of cold-water immersion on health and wellbeing: A systematic review and meta-analysisCain T, Brinsley J, Bennett H, et al.. PLOS ONE, 2025.Read the paper ↗PubMed ↗ Every entry in that analysis came from one Lithuanian lab. In its studies, men either sat in 14°C water for 10 minutes or went through on-and-off immersions over 170 minutes. The review's results don't name the stress marker. The Lithuanian studies measured cortisol and adrenaline-type hormones (catecholamines), and cortisol falls naturally over the course of a day.Source 4 · Crossover trialResidual effects of short-term whole-body cold-water immersion on the cytokine profile, white blood cell count, and blood markers of stressEimonte M, Paulauskas H, Daniuseviciute L, et al.. International Journal of Hyperthermia, 2021.Read the paper ↗PubMed ↗

Immune markers showed no effect at 0 or 1 hour.Source 1 · Meta-analysisEffects of cold-water immersion on health and wellbeing: A systematic review and meta-analysisCain T, Brinsley J, Bennett H, et al.. PLOS ONE, 2025.Read the paper ↗PubMed ↗ Sleep and quality of life got one study each. The quality-of-life result is the cold-shower trial at 30 days. For sleep the review used a 1–5 self-rating (3.6 against 3.1) from a heat-training study, and that study's own abstract reports minimal effect on sleep.Source 5 · Randomized trialSleep quantity and quality during consecutive day heat training with the inclusion of cold-water immersion recoverySkein M, Wingfield G, Gale R, et al.. Journal of Thermal Biology, 2018.Read the paper ↗PubMed ↗ The one trial that measured mood found no effect.Source 1 · Meta-analysisEffects of cold-water immersion on health and wellbeing: A systematic review and meta-analysisCain T, Brinsley J, Bennett H, et al.. PLOS ONE, 2025.Read the paper ↗PubMed ↗

The study can't tell you these things

  • It pooled changes within the cold groups, so each estimate compares people with their own earlier readings and leaves the control groups out.
  • Apart from the shower trial, every study was small and all-male.
  • Several headline outcomes draw on only one or two studies.
  • The stress analysis doesn't name the marker it pooled, and all its data come from one lab.
  • The text and the forest plot print the immediate stress estimate with opposite signs.

People quote it like this

The abstract concludes that cold water has time-dependent effects on stress, immunity, sleep and quality of life. Several of those effects have only one study behind them, and the pooled inflammation markers went up.Source 1 · Meta-analysisEffects of cold-water immersion on health and wellbeing: A systematic review and meta-analysisCain T, Brinsley J, Bennett H, et al.. PLOS ONE, 2025.Read the paper ↗PubMed ↗

We cited these sources

  1. 01Cain T, Brinsley J, Bennett H, Nelson M, Maher C, Singh B. Effects of cold-water immersion on health and wellbeing: A systematic review and meta-analysis. PLOS ONE. 2025;20(1):e0317615. doi:10.1371/journal.pone.0317615 PMID 39879231
  2. 02Buijze GA, Sierevelt IN, van der Heijden BCJM, Dijkgraaf MG, Frings-Dresen MHW. The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial. PLOS ONE. 2016;11(9):e0161749. doi:10.1371/journal.pone.0161749 PMID 27631616
  3. 03Earp JE, Hatfield DL, Sherman A, Lee EC, Kraemer WJ. Cold-water immersion blunts and delays increases in circulating testosterone and cytokines post-resistance exercise. European Journal of Applied Physiology. 2019;119(8):1901-1907. doi:10.1007/s00421-019-04178-7 PMID 31222379
  4. 04Eimonte M, Paulauskas H, Daniuseviciute L, Eimantas N, Vitkauskiene A, Dauksaite G, et al.. Residual effects of short-term whole-body cold-water immersion on the cytokine profile, white blood cell count, and blood markers of stress. International Journal of Hyperthermia. 2021;38(1):696-707. doi:10.1080/02656736.2021.1915504 PMID 33910456
  5. 05Skein M, Wingfield G, Gale R, Washington TL, Minett GM. Sleep quantity and quality during consecutive day heat training with the inclusion of cold-water immersion recovery. Journal of Thermal Biology. 2018;74:63-70. doi:10.1016/j.jtherbio.2018.03.012 PMID 29801652