Lady Gaga. Madonna. Chris Hemsworth (aka Thor). They all do it.

And while the benefits of plunging into frigid water abound on social media – improved mood and sleep, relief from muscle aches, weight loss – they’re not well documented in scientific and medical literature.

Intuitively, the practice seems risky; the phrase “heart-stopping cold” pops to mind.

So we turned to one of our experts, Hanna (“John”) Slim, MD, a cardiologist at University of Vermont Health - Champlain Valley Physicians Hospital and Alice Hyde Medical Center, for his thoughts.

“I’m always very cautious when people on TV or social media come out super-confident about the benefits of something,” says Dr. Slim. “In this case, I don’t think anyone can say with certainty that there are any health benefits as of yet.”

Dr. Slim notes that most of the studies he’s seen about the benefits of cold plunging have been very limited, and their methodologies questionable. “The studies are either too small, or they’ve been observational studies, which are not randomized or placebo-controlled,” he explains. Because participants in these studies know they are receiving a treatment with supposed benefits, they might imagine positive results that can’t be independently verified.

Dr. Slim does have some words of advice for anyone interested in trying it out.

“People who have established heart disease or who are at risk for a heart attack should definitely not do it,” he says. Cardiac risk factors include diabetes, high blood pressure, smoking and having a family history of heart disease.

Why Cold Plunging Stresses the Heart

Immersing your body in ice cold water produces a shock response, Dr. Slim explains. “Your heart rate goes up, your blood pressure goes up and you would hyperventilate. For people who have heart disease, a sudden rise in heart rate and blood pressure can destabilize an already existing plaque in their arteries, and potentially cause a heart attack. That’s the big concern.”

Also, when you expose your skin to cold temperatures, your blood vessels constrict. “Your body shifts fluids away from the extremities and toward the center of the body. For people who already have heart failure, those fluids can go into the lungs. Even people who don’t have heart failure can get into trouble,” he says.

He offers a real-life example: the well-documented increase in heart attacks when people start shoveling snow in the winter. “We think it’s due to the combination of acute exposure to cold weather and breathing cold air, combined with doing a strenuous activity without warming up. A shock response is very similar,” he explains.

Is Cold Plunging Safe?

For people who are confirmed to be free of heart disease or cardiac risk factors, Dr. Slim says he’s not necessarily against the practice, but he advises people to use common sense. Even for people who are young and healthy, there are still some safety concerns.

For instance, if you’re not used to doing cold plunges routinely, you put yourself at risk of drowning. As soon as you go underwater, the cold shock triggers a rapid increase in breathing, which could cause you to involuntarily inhale. Hyperventilation can also sometimes trigger seizures. And finally, there is also a risk of hypothermia, which, even in the early stages, makes it harder to think clearly.

“Definitely don’t do it alone. You want someone with you,” Dr. Slim advises.

He suggests that, if you really want to try cold plunging, start slow. Immerse yourself for a shorter period of time in cold, but not icy, water, then gradually increase the duration and/or decrease the temperature. He notes that he can’t offer any specifics on number of minutes or water temperatures, because everyone is different.

For this reason, he strongly suggests that people consult with their doctors first.

Trendy Doesn’t Mean True

In short, Dr. Slim says, cold plunging is a trend. Whether it will pan out eventually, only time will tell.

“At this point, claims that cold plunging boosts your immunity or accelerates muscle recovery are just theories. Any of us could come up with a logic behind it that makes it make sense, but that doesn’t mean it’s true.” Large scale studies are needed to help us better understand the risks and benefits before making recommendations.

But, he says, he doesn’t mean to throw cold water on something that many people enjoy. “If it’s something that makes you feel good, then by all means – enjoy it. Just use common sense.”