This Is What Happens to Your Body When it's Shocked by Freezing Water

Everybody lines up on the sand. Steam broils out of their nostrils into the 40-degree morning air, and they adjust their bathing suits and brace themselves. The water is even colder. With a yelp and a shiver, everyone walks down the Coney Island beach and into the Atlantic Ocean. They're members of the oldest, but not only, polar bear club in the US, and this is what they do—on purpose—every Sunday.

“Let's just start off by saying it's damn cold,” says Dennis Thomas, president of the Coney Island Polar Bear Club, established in 1903. “There's no question about that.” Thomas has been taking the plunge for more than 30 years, and says he never gets used to it. Winter water temperatures range from the low 30s on Lake Michigan where the Chicago and Milwaukee polar bear clubs swim, to the oceanic mid- and upper-30s where the New York and Seattle polar bear clubs swim.

Everyone shouts and splashes around for a while and then staggers back up the beach toward towels and hot cocoa. If you've seen the photos, you know they don't look miserable, somehow, but happy. “There's a little bit of evidence suggesting that people have a dopamine response [to cold water immersion],” says Jon Rittenberger, an associate professor of emergency medicine at the University of Pittsburgh.

Dopamine, like serotonin, is one of the neurotransmitters the brain releases that causes feelings of happiness and contentedness. For two or three days afterwards, Thomas says, people who take the polar bear plunge often talk of feeling invigorated, like they've downed a shot glass of pure energy, with an overlaying sense of calm. “I've met a lot of people [who do it] who've said they hate the winter,” he says. “They needed to find some way to value and embrace it.” Of the club's 120 members, 80 to 90 turn out every week. They're hooked.

Releases of dopamine and serotonin in response to exercise are well-documented, Rittenberger says, and that includes cold-water exercise where a person works out in an icy cold pool. But there's a lack of clarity as to how much of that dopamine and serotonin—in this case—is due to the cold water and how much is due to the simple fact that these people are exercising.

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Doctors, by and large, say there's no evidence that polar bear plunges actually do the body any good beyond these feelings, and that these swims can be dangerous. Sudden immersion in cold water can trigger a heart attack, stroke, or hyperventilation, and even good swimmers can drown as muscles become paralyzed from the frigid water, Rittenberger says.

Even where the more southerly polar bear clubs swim in San Francisco and the Carolinas, water temperature in the mid-50s is still cold enough to induce hypothermia. The thermal capacity of water is far greater than the thermal capacity of air, meaning that water can pull the heat out of you about 20 times more efficiently than air can, Rittenberger says. The Centers for Disease Control and Prevention says cold water steals heat even faster than that, at about 25 times more efficiently than cold air.

Other than being struck by lightning, cold shock rates among the biggest jolts your body can experience, according to the National Center for Cold Water Safety, a nonprofit founded by Moulton Avery, the past director of the Carolina Wilderness Institute survival skills school. It's why swimmers new to polar bear plunges should take it slowly and go with experienced polar bear swimmers.

It's also why all swimmers tend to walk down the beach into the water gradually, rather than plunge suddenly into a deep lake or harbor. Beyond the initial shock, Thomas says that if you can make it three minutes in such cold water then you can probably make it for 10, although he says that's about the upper limit.

For the first 10 minutes or so, the body compensates for the cold by shunting blood to its core and decreasing blood flow to the skin, Rittenberger says, but after 10 to 15 minutes you'll start to have problems with your nerves. Their ability to conduct the electrical impulses that let your brain move muscles diminishes, and that can make it hard to swim and hard to exit the water. From 15 to 30 minutes is where your body's ability to conserve its core temperature begins to fail drastically. Hypothermia sets in, and critical problems start to cascade. “The one that tends to kill people,” Rittenberger says, “is the fact that it causes your heart to stop beating.”

Thomas, the 30-year veteran of the plunges, says he's never seen anyone roll over with a heart attack. Swimmers, in deep winter, tend to exit the water after 10 minutes to avoid the types of symptoms that Rittenberger describes. There are no hard and fast rules as to who can or can't join the Coney Island Polar Bear Club, but Thomas emphasizes that going with an experienced group means everyone looks out for each other. If you were to hit the beach alone or with only a couple of friends and one or two of you came down with cold-induced muscle paralysis, your chances of surviving would not be very good.

With some advance planning, you can prep your body to tolerate the cold water by taking cold baths or swimming in a cold-water pool. “The body has some capacity to acclimate [to heat and cold], Rittenberger says. "There's some evidence suggesting that people repeatedly exposing themselves (to cold water) handle it better and acclimate to it."

Part of the Wim Hof Method consists of incorporating cold showers into your daily routine, although the Method exists on claims for general well-being and not specifically to cold water swimming. Easing into it is key. If you're not used to cold showers—and who is?—then it recommends finishing your normal warm showers with 30 seconds of cold water, and you'll “quickly notice that you are able to tolerate the cold more and more”, the authors write. Still, those who plunge regularly see it as an unnecessary complication of a simple thing. “No one really does any serious preparation,” Thomas says, adding that he despises cold showers and would never sit in a bathtub of ice water. Most swimmers just show up and do it.

Membership to the Coney Island Polar Bear Club is closed because Thomas fears larger numbers would hurt the group's close-knit nature, but every year the Coneys, like polar bear clubs everywhere, hold a New Year's Day swim open to everyone. In New York, Thomas says they get about 2,500 swimmers every January 1st. That's the best time to go, Thomas says—when there are experienced polar bear swimmers around to watch your back. And to splash cold water at it when you're not looking.

Correction 1/3/18: After further thought, Jon Rittenberger felt the research wasn't strong enough to uphold his original statement about the anti-inflammatory effects of repeated plunges. The quote has been amended.

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