The coolest thing on social media these days might be celebrities and regular folks plunging into frigid water or taking ice baths.
The touted benefits include improved mood, more energy, weight loss and reduced inflammation, but the science supporting some of those claims is lukewarm.
Kim Kardashian posted her foray on Instagram. Harry Styles has tweeted about his dips. Kristen Bell says her plunges are “brutal” but mentally uplifting. And Lizzo says ice plunges reduce inflammation and make her body feel better.
Here’s what medical evidence, experts and fans say about the practice, which dates back centuries.
The mind
You might call Dan O’Conor an amateur authority on cold water immersion. Since June 2020, the 55-year-old Chicago man has plunged into Lake Michigan daily, even on frigid mornings when he has to shovel through the ice.
“The endorphin rush … is an incredible way to wake up and just kind of shock the body and get the engine going,” O’Conor said on a recent morning when the air temperature was a frosty 23 degrees.
Endorphins are “feel good” hormones released in response to pain, stress, exercise and other activities.
With the lake temperature 34 degrees , the barechested O’Conor did a running jump from the snow-covered shore to launch a forward flip into the icy water.
“My mental health is a lot stronger, a lot brighter,” O’Conor said. “I found some Zen down here coming down and jumping into the lake and shocking that body.”
Dr. Will Cronenwett, chief of psychiatry at Northwestern University’s Feinberg School of Medicine, tried cold-water immersion years ago while visiting Scandinavian friends on a Baltic island. After a sauna, he jumped into the ice-cold water for a few minutes and had what he called an intense and invigorating experience.
“It felt like I was being stabbed with hundreds of millions of really small electrical needles,” he said. “I felt like I was strong and powerful and could do anything.”
But Cronenwett said studying cold-water immersion with a randomized controlled trial — the gold standard in medicine — is challenging because devising a placebo for cold plunges could be difficult.
Cronenwett said cold-water immersion stimulates the part of the nervous system that controls the resting or relaxation state and that that might enhance feelings of well-being.
It also stimulates the part of the nervous system that regulates fight-or-flight stress response. Doing it on a regular basis might dampen that response, which, in turn, could help people feel better able to handle other stresses in their lives, though that isn’t proven, he said.
Czech researchers found that cold water plunging can increase blood concentrations of dopamine — another so-called happy hormone made in the brain — by 250%. High amounts have been linked with paranoia and aggression, according to physiologist James Mercer, a professor emeritus at the Arctic University of Norway who coauthored a recent scientific review of cold-water immersion studies.
The heart
Cold-water immersion raises blood pressure and increases stress on the heart. Studies have shown this is safe for healthy people and that the effects are temporary.
But it can be dangerous for people with heart trouble, sometimes leading to life-threatening irregular heartbeats, Cronenwett said. People with heart conditions or a family history of early heart disease should consult a doctor before plunging, he said.
Metabolism
Repeated cold-water immersions during winter months have been shown to improve the way the body responds to insulin, a hormone that controls blood-sugar levels, Mercer noted. This might help reduce risks for diabetes or keep the disease under better control in people already affected, though more studies would be needed to prove that.
Cold-water immersion also activates brown fat — tissue that helps keep the body warm and helps it control blood sugar and insulin levels. It also helps the body burn calories, which has prompted research into whether cold-water immersion is an effective way to lose weight. The evidence on that so far is inconclusive.
Immune system
Anecdotal research suggests that people who routinely swim in chilly water get fewer colds, and there’s evidence it can increase levels of certain white blood cells and other infection-fighting substances. Whether an occasional dunk in ice water can produce the same effect is unclear.
One final note
Among the biggest unanswered questions: How cold does water have to be to achieve any health benefits? And will a quick dunk have the same effect as a long swim?
“There is no answer to ‘the colder the better,’” Mercer said. “Also, it depends on the type of response you are looking at. For example, some occur very quickly, like changes in blood pressure. ... Others, such as the formation of brown fat, take much longer.”
