Polar plunges aren’t just for the daring

On January 1, some hardy souls will greet the new year not by nursing a champagne hangover in bed, but by plunging into frigid water. In New York City, thousands of people participate in a seaside “polar plunge” held annually since 1903. Similarly bone-chilling swims take place across the country and overseas on New Year’s Day.

These brave revelers may be on to something. Icy immersion isn’t without risk, and there’s no single temperature range used to study dunking or swimming. But a growing body of science suggests cold water may hold benefits for mental and physical health alike.

Lee Hill, an exercise physiologist at McGill University in Montreal, has a long history with cold-water swimming. A former competitive swimmer and coach, Hill used to take kilometers-long swims, sometimes in water below 10° Celsius, in their native South Africa. Though not for the faint of heart, these chilly dips create an unmatched feeling, Hill says. “You feel Zen. … You feel every part of your body. You’re aware of your breathing. You forget about everything [else].”

Diving into icy cold water triggers a pair of conflicting physiologic responses, says James Mercer, a professor emeritus at the Arctic University of Norway in Tromsø who has studied cold-water swimming. One is the “diving response,” which is meant to conserve oxygen underwater. Heart rate slows, breathing is inhibited, blood vessels constrict, and blood flow is shunted to critical organs. The second is the “cold shock response,” Mercer explains. “Your heart rate goes through the roof. Your blood pressure goes through the roof. You’re gasping for breath,” he says.

That push-and-pull may sound hard on the body, and it can be dangerous, particularly if you have underlying heart issues or aren’t prepared for the strain on your system. (If you’re polar plunging for the first time, go with a buddy, ease in slowly, get out of the water within five to 10 minutes and know the warning signs of hypothermia, Hill says.) But stress isn’t always a bad thing, Mercer says. It’s how the body builds resilience. The research on cold-water exposure isn’t perfect, Mercer says; studies tend to be small and poorly controlled, and their designs vary widely in terms of participant characteristics, water temperature, and duration and type of activity. That makes it hard to definitively prove the practice has benefits, or to say whether swimming in cold water is better you than, say, taking an ice bath or a quick plunge.

Nonetheless, some research finds that regular, prolonged immersion in cold water makes the body more resilient. For example, young men who endured daily hour-long baths in 13° to 15° C water for seven days got a physiological boost at the end of the trial, researchers reported in 2024 in Advanced Biology. Specifically, their cells did a better job of clearing out old or damaged parts, a process thought to help prevent various diseases and maintain overall cellular function.

Other research suggests regular cold-water immersion may activate the immune system, potentially boosting white blood cell counts and plasma concentrations of immune proteins.

It may be hard for science to pin down what exactly makes cold-water swimming so powerful, says psychobiologist Mark Wetherell of Northumbria University in England. Wetherell recently published a small study in Lifestyle Medicine, finding that cold-water swimmers report lower anxiety, higher self-confidence, better sleep and other psychological benefits on days they dip.

Rather than a single mechanism, Wetherell thinks many factors contribute to those boosts: cold water, exercise, time outdoors, social support (since most people swim with others), the thrill of doing something wild enough to win bragging rights — and an adrenaline rush.