What actually happens to your body when you cool it? When you enter a cryotherapy chamber and your skin encounters the shockingly cold air, immediately your blood beats a fast retreat. In a process known as "vasoconstriction," your body tries to conserve heat by shifting blood away from your extremities to its core. That's why your fingers and toes go numb first when you get cold.
After four minutes in a cryochamber at minus 166 degrees Fahrenheit (minus 110 degrees Celsius), your skin temperature drops to about 66.2 degrees Fahrenheit (19 degrees Celsius). Your nerve speed slows with lowering skin temperatures, your blood flow decreases, metabolism slows and power output goes down. If you're not careful, you can get frostbite [source: Costello et al.].
A 2015 study reviewed the scientific literature on the claims that cryotherapy could, at the very least, reduce muscle soreness after exercise. The researchers found four studies so small that the total number of participants came to only 64. Pooling the data revealed that while the studies themselves concluded cryotherapy provided some benefit, the actual evidence didn't produce a clear result. The pool of participants was too small, the subjects too homogeneous, the methods too varied and the data too limited [source: Costello et al.].
In other words, there is as yet no good scientific evidence to show that cryotherapy is helpful. Further, a 2012 study comparing whole-body cryotherapy at the above-mentioned temperature with an ice bath at 46 F (8 C) found no difference between the two. And while the study concluded that cooling off might provide some slight reduction in muscle soreness, there was no evidence that either treatment aided recovery. So, if you insist on freezing your buns in order to de-ache, you might as well jump in a tub of ice-cubes — it's a lot cheaper [source: Costello et al.].
Just be careful — if your internal body temperature drops below 95 degrees Fahrenheit (35 degrees Celsius), you've got mild hypothermia. This happens 25 times faster if you're in water than if you're dry [source: Rettner]. In fact, that's one of the benefits touted by cryotherapy proponents. Because a cryotherapy chamber uses very dry air to cool you down, the risk of hypothermia is relatively low. That said, a cryosauna is not a place to hang out. According to the National Weather Service, at minus 60 degrees Fahrenheit (minus 51.1 degrees Celsius) you can get frostbite in 10 minutes, even if there's little to no wind [source: Sterbenz].
One caveat: So far, the only scientifically proven benefit of body-cooling is for oxygen-deprived newborns. It may be that slight hypothermia can help prevent cell self-destruction and activate neural-protective genes [source: Rosen]. But the evidence for this is so situation-specific, it can't automatically be applied to the general population.