Short read
Cain and colleagues at the University of South Australia published this systematic review and meta-analysis in PLOS ONE in 2025, registered in advance with PROSPERO under CRD42024500591. It included randomised trials in healthy adults aged 18 and over using cold showers, ice baths or plunges at 15 degrees or less for at least 30 seconds. The modality is cold water, not sauna. 11 trials with 3177 participants met the criteria; 10 used baths and 1 used showers, with water between 7 and 15 degrees and exposures from 30 seconds to 2 hours.
The pooled values compare the same people before and after cold exposure. Measured that way, inflammation markers were higher immediately afterwards, a standardised mean difference of 1.03 (0.37 to 1.68), and still higher after one hour, 1.26 (0.59 to 1.94), an acute inflammatory response. Stress was lower at 12 hours, minus 1.00 (minus 1.40 to minus 0.61), but showed no robust effect immediately or at 1, 24 and 48 hours. There was no pooled effect on immune function. Sleep and life quality got better, while mood was unchanged. The narrative summary cites 29 percent less sickness absence among cold showerers, a figure from a single controlled study, not from the meta-analysis.
The authors name the main limit themselves: only 11 randomised trials, small samples and little diversity in the populations studied. 6 trials tested a single exposure, and 5 applied cold after exercise, which mixes recovery with the effect of the cold. The protocols differ widely, and none of the pooled values is a comparison with an untreated parallel group.
Two findings shape how the data can be reported. Inflammation rose at first rather than fell, so the evidence does not support cold as an immediate anti-inflammatory. And the stress effect appeared only after 12 hours.