Cold Facts

One of winter’s goofiest traditions is jumping into a freezing body of water. Here’s what happens when you take a polar plunge.

What happens to your body when you dunk it in near-freezing water? We investigate the science of shock.

PICTURE, FOR A moment, walking into an ice-cold lake. Your feet are ground zero for the shock wave that goes through your body, and your brain tells you to get the hell out of there. But in you go anyway, because you’re polar plunging. These acts of wintertime daredevilry are gaining in popularity. Some strip down to celebrate the New Year, or to raise money for charity, like Plungefest in Annapolis, Maryland, where people including Adam Hays, a Special Olympics athlete, are deemed Super Plungers, for going in every hour for an entire day. And interesting things happen when your body goes into a cold-shock response, according to John W. Castellani, a research physiologist in the Thermal and Mountain Medicine Division at the U.S. Army Research Institute of Environmental Medicine, starting with your feet freezing and your heart pounding out of your chest. And there’s more.