In one unusual but revealing study, his researchers repeatedly immersed one side of people's bodies until it showed evidence of habituation, while keeping the other side warm -- and then turned them over and immersed the side that had never been in the cold water and found that there was still a significant reduction in their cold shock response.

CNN: Are polar bear plunges good for you?

Tipton, who conducts research on the human body's physiological and psychological response to adverse environments, found that it takes as few as five immersions in icy water for the body to develop a tolerance that can reduce the risk of cold-shock response by half.

CNN: Are polar bear plunges good for you?

That's caused by the adrenaline and stress hormones that the body releases in response to the shock of the cold temperature, but experts say that these rushes are not as healthy as people think.

CNN: Are polar bear plunges good for you?