There’s Only One Reason to Cold Plunge

Cold-­water bathing has a long history as a health hack. The ancient Greeks and Romans partook to treat fevers. Eighteenth-­century mental institutions employed a tactic called the bain de surprise, suddenly dunking their patients in cold water to jolt them out of their depression or psychosis. (Some doctors aimed to wet only the head to cure “hot brain.”) Last year, Mehmet Oz, the celebrity doctor who is now the head of Medicaid and Medicare, posted an Instagram video of himself in a one-man ice bath, promoting it as a possible boon for immunity and longevity. “Maybe you affect how the mitochondria work,” he says, before dunking his head into the bath and then flipping his hair as “Careless Whisper” plays in the background. Maybe. Certainly the plunge has a bit of logic behind it. Cold exposure dampens inflammation, which can contribute to a person’s risk of heart disease and cancer. In nature, some very long-lived animals, such as the bowhead whale (lifespan: about 200 years) and the Greenland shark (500 years) basically cold plunge for their entire life. In fact, cold water does seem to provide some benefits for humans as well—just not the ones that Oz and other wellness enthusiasts most loudly promote. Cold-­plunge partisans claim, for instance, that cold exposure activates “brown fat,” a special type of fat tissue that burns energy to generate heat. Activating this fat is said to convey almost-magical health benefits, reducing the risk of diabetes and other chronic diseases. Casey Means, President Trump’s pick to be surgeon general, pointed to brown fat when explaining to her followers why she’s come to “LOVE cold plunges” in a 2024 Instagram post. Unfortunately, most adults typically have only a few grams of brown fat, so any beneficial effect from activating it is likely quite small. Even a study of Wim Hof, the Dutch health guru nicknamed “The Iceman” who helped popularize ice bathing, proved disappointing: Using fMRI and other imaging techniques, researchers found that his brown-fat activation after a session of his Wim Hof Method (breathing exercises plus extended cold plunging) was “unremarkable.” (In an email to The Atlantic, Hof acknowledged that brown fat is not primarily responsible for warming the body in cold environments, but said that his breathing techniques support muscular activity that functions as a “physiological radiator.” He did not elaborate on the health effects of said muscular activity or cold plunging more generally.) [Read: How cold can a living body get?] Cold plunging has also been touted as a workout-recovery tactic. It took off after Paula Radcliffe, once the fastest women’s marathoner of all time, told BBC Sport in 2002 that post-race ice baths were her secret weapon. Michael Phelps and LeBron James have carried the torch, and photos of pained athletes sitting in icy tubs have become a social-­media staple, spreading the practice to the common gym goer. Last month, Health and Human Services Secretary Robert F. Kennedy Jr. posted a workout video (co-starring Kid Rock) in which he does push-ups and rides an exercise bike in a sauna, then does a cold plunge in his jeans. (HHS did not return a request for comment.) Although a handful of studies suggest that cold-­water immersion may help reduce feelings of muscle soreness after exercise, it also seems capable of limiting your gains. Some studies have shown that cold-­water immersion immediately after resistance exercise ­reduces gains in muscle size and strength. One 2015 study found that cold plunging after resistance training reduced muscle growth by 20 percent. Cold plunging has grown so popular that it seems to be almost mandatory at many North American sauna establishments. In some, guides wield timers and even whistles to ensure that patrons realize the full health benefits of “contrast therapy,” moving from a hot sauna to an icy-cold plunge and back again. But research suggests that the hot part of contrast therapy ­may be more helpful for muscle health and exercise gains, and that intermittent cold plunging may even neuter those benefits. For example, the cardiovascular and cellular benefits of heat adaptation typically take place when the core body temperature reaches about 101.3 degrees Fahrenheit. But many contrast-therapy regimens march their adherents into a cold plunge immediately after the hot sauna, which pulls their core temperature down before it can rise to the sweet spot. The current trend in the NBA, for instance, is to toggle between 15-minute infrared-sauna sessions and three frigid minutes of plunge. In fact, recent research suggests that heat alone is a better exercise-recovery tool than ice or cold water. A 2017 clinical trial had volunteers perform an hour of “exhaustive” arm-cycling intervals (think stationary bikes but with handheld cranks instead of pedals). They recovered far better from this ordeal when their arms were warmed rather than cooled. In yet another study, researchers found that cold-­water immersion did nothing for subjects with laboratory-­induced muscle damage, whereas warm water speeded healing and reduced soreness. Perhaps that’s because warm water (or a warm sauna) opens blood vessels, increasing blood flow to the tired or injured muscles. It also activates heat-shock proteins, which repair damaged cells. Cold water, however, does the opposite—constricting blood flow, blunting repair mechanisms, and making muscles and connective tissue less elastic. [Read: How did healing ourselves get so exhausting?] Even the doctor who popularized the RICE injury-recovery protocol in the 1970s—­rest, ice, compression, and elevation—­has recanted the “ice” part, after it became clear that inhibiting inflammation can also inhibit healing. In the 2010s, researchers found that transient inflammation created by exercise (and other short-term stressors) acts as a signaling mechanism that helps marshal the body’s own healing response, while also spurring the strength and endurance improvements brought on by exercise. Still, many if not most of the published studies on cold plunging, including those that undermine its hype, are quite small, with 20 subjects or fewer, the large majority of whom were healthy, fit young men likely volunteering for studies at universities they attended. Relatively few subjects were female, or old enough to be president. These studies also tended to be short-­term, sometimes involving only a single ice bath or hot-­water-­immersion session. And for obvious reasons, carrying out a truly blind study of cold (or heat) exposure is impossible. The popularity of cold plunging may come down to the simple truth that it makes some adherents feel good. In the only truly large-­scale cold-water study, done in the Netherlands, researchers told more than 3,000 people to take cold showers. They ranged in age from 18 to 65, and they were randomized to end their usual daily shower with 30, 60, or 90 seconds of cold water for a month. The study wasn’t designed to measure brown-fat activation or muscle recovery, but it did reveal that the cold showerers missed about 30 percent fewer workdays than a control group who took only hot showers every day. Both groups reported the same number of total illness days—but for whatever reason, the cold showerers seemed more motivated to go into work. The amazing thing about this study, however, was that many of the subjects voluntarily continued with the cold showers after the initial 30-day study period expired—although they, presumably, were no longer being compensated for participating in the study. This may speak to why some people swear by cold plunges and showers with an almost-religious fervor. They get hooked. “That sudden fall in skin temperature releases quite a lot of stress hormones, and ends up releasing serotonin. So you get a feel-good factor,” Mike Tipton, a professor of extreme physiology at the University of Portsmouth who has studied cold-water immersion for decades, told me. “It’s the thing that makes you feel alive.” Perhaps the most consistent reported benefit of cold-water exposure is its effect on mood and mental health. People do it because, for some reason, it makes them feel better. I struggle with cold plunging, mostly because I dislike cold water and pain, and being hounded into doing things. To me, a plunge usually feels best when it is over. I began to see the appeal only after a 2024 experience at Sauna Days, an eclectic gathering that’s like a music festival, but with wood-burning saunas instead of bands, held near the shores of Lake Superior, the deepest, rockiest, and coldest of the Great Lakes. I was initially happy to sleep through the early-morning swims that most other attendees were partaking in—I was there for the saunas—but eventually, the combination of a sunny day, the coaching of a friend, and latent FOMO led me to the water. At the rocky shore, I gingerly waded in and squatted, keeping my hands and, crucially, my nipples out of the 43-degree water. To my surprise, I felt relief rather than pain, as I unloaded all of that pent-­up sauna heat into the chilly lake water. I dunked myself neck-­deep and let out a deep, satisfying sigh. Submerged in Lake Superior, I realized that viewing cold plunging as so many of its champions suggested—through the lens of health optimization, as a purely physical practice wrapped in bro science—had been a mistake. That wasn’t it at all. It was really more about changing your mental state, knocking you out of whatever spiral you happen to be stuck in—­rather like a bain de surprise. (To be fair to Oz, he mentions this upside too: Plunging is a reminder, he says, that “your mind is strong and your body can keep up.”) My second mistake had been to think of plunging as a purely solo activity. My Instagram Reels are replete with longevity bros (and babes) dunking themselves in one-person cold plunges that resemble high-design coffins. But I found that the cold was much easier to take with company, which turned it into a bonding experience, as opposed to ritual self-punishment. I had to admit, splashing around in water cold enough to induce hypothermia had a certain thrill. I felt a little naughty. And I felt even better when I got out. This article has been adapted from Bill Gifford’s forthcoming book, Hotwired: How The Hidden Power of Heat Makes Us Stronger.