Whole-Body Cryotherapy

Whole-body cryotherapy means standing for a few minutes in a chamber of extremely cold air, sold for faster recovery after exercise. It chills the skin fast but cools deep tissue far less than cold water does, and the Cochrane review of it found too little evidence to say whether it reduces muscle soreness at all — from four small trials that never actively looked for side effects.

Treat cryotherapy as unproven for recovery: the evidence can't show that it reduces soreness. If you want cold for soreness, cold water has the larger evidence base.

What it is

A cryotherapy chamber holds air at −110 to −195 °C, and a session lasts 2–4 minutes. Air carries heat away far more slowly than water — water pulls heat from the body roughly 24 times faster — so the chamber drops skin temperature quickly but does not reach the deep-tissue or core cooling of an ice bath. It is a different stimulus from cold-water immersion, and evidence about one does not transfer to the other.

The main evidence: one review, four small trials

The dedicated Cochrane review — the standard systematic review used in medicine — pooled four laboratory trials in 64 physically active adults with a mean age of 23. All but four of them were men, so there is essentially no evidence in women or in elite athletes.^[1]

Its verdict was that the evidence is insufficient to determine whether cryotherapy reduces muscle soreness or improves how recovered people feel, compared with rest or no treatment.

Only one timepoint separated from control. One hour after the session, self-reported soreness was lower by a moderate-to-large amount (a standardised mean difference of −0.77, where about 0.5 counts as moderate and 0.8 as large). That rested on 20 participants in two crossover trials.
The later timepoints are compatible with no effect. At 24, 48 and 72 hours the confidence intervals — the range where the true effect most plausibly lies — straddled zero.
Every result is very low certainty. All four trials carried a high risk of bias, and every outcome was graded very-low-certainty.

What has never been tested

Cryotherapy against cold water. No trial has compared the two. The only active comparator ever tested was far-infrared therapy, in a single crossover trial of nine runners.
Different doses. No trial compared temperatures, session lengths or schedules.
Safety. None of the four trials ran active surveillance for adverse events, which the review's authors flagged as a real gap given the temperatures involved. No harm being reported is not the same as no harm.

Safety

The temperatures are the most extreme of any cold practice, and frostbite is a recognised risk at very low temperatures. The conditions that rule out cold water — a heart-rhythm disorder, severe Raynaud's, cold urticaria, cryoglobulinaemia, unstable heart disease — are listed on Cold exposure; no cryotherapy trial has looked at them.

Immune cells: movement, not "boosted immunity"

Cryotherapy does move immune cells around. In a trial that randomised 26 men to three minutes of partial-body cryotherapy at −110 to −140 °C, three minutes in 9 °C water, or a 24 °C control, cytotoxic (CD8+) T-cell counts in the blood rose after exposure — most after the cryotherapy, more than after either the cold water or the control. A rise in circulating natural-killer cells, traced to their cytotoxic subset, was seen after cryotherapy only.^[2]

That is cells leaving their resting reservoirs and passing through the bloodstream, not evidence of a stronger immune system. Partial-body cryotherapy also differs from the whole-body chambers, and the trial was small and preliminary.

What to do

Don't rely on cryotherapy for recovery. The review could not show that it reduces soreness, and no trial has compared it with cold water.
If you want cold for soreness, use water — see Cold exposure for the doses and the caveats, including how much of the effect is expectation.
If you go anyway, know that safety is unstudied. The trials never looked properly for side effects at these temperatures.