Cold plunges: signal, stress and hype.

Image: Unsplash. Editorial illustration; it does not depict the study participants.

What caught our attention

A 2025 systematic review and meta-analysis examined randomised trials of cold-water immersion in healthy adults. Eleven studies involving 3,177 participants were included, covering cold showers, baths and plunges at 15°C or below.

The surprising bit

The review found an acute increase in inflammatory markers immediately and one hour after immersion rather than a simple immediate “anti-inflammatory” effect. It also found reduced stress at 12 hours, but not immediately, one hour, 24 hours or 48 hours after exposure.

Where the signal gets interesting

The authors reported narrative evidence of improvements in sleep quality and quality of life in some studies, while pooled acute immune-function measures were not significant. One cold-shower study reported reduced sickness absence, but that does not establish a universal immune-boosting effect.

What we still don't know

The evidence base remains constrained by relatively few randomised trials, small samples for several outcomes and limited diversity. Optimal temperature, duration, frequency and long-term effects are still open questions.

Why we are watching it

Cold exposure is a perfect Youtopia topic: accessible, biologically active, culturally hyped and scientifically unfinished. Rather than asking whether cold plunges “work,” the better questions are: for what outcome, at what dose, at what time point, and compared with what?