There isn’t much data on global or nationwide sauna use, but the market does seem to have revived, driven mainly by users seeking health benefits. “There’s a movement now,” said Eero Kilpi, president of the North American Sauna Society, who pointed to commercial saunas popping up as well as sales of portable, mobile saunas, which people can put in their backyard or take on a camping trip.

As saunas become trendy, companies often promote them with the promise of health benefits such as “detoxification”, heart health and increased metabolism, along with claims that the heat can simulate a workout without the work.

There is some research that suggests a trip to the sauna may have some health benefits — but you shouldn’t believe every claim you hear, said Earric Lee, a researcher at the University of Jyväskylä in Finland who has studied their health effects.

Although several studies point to the potential benefits of saunas, some of the most prominent research focuses on data from men in Eastern Finland, as part of an ongoing study on risk factors for heart disease. Observational studies have found intriguing links between regular Finnish-style sauna bathing and lower risks of cardiovascular issues and inflammation, although the studies cannot definitively prove causation and focus on a specific slice of the population (middle-aged and older Finnish men).

Still, the findings suggest that saunas may help improve cardiovascular function, said Setor Kunutsor, an associate professor at the University of Leicester in England who has been involved in some of these studies. That may be because short bouts of intense heat stress our heart in beneficial ways — and strengthen the cardiovascular system over time, Kunutsor said.

When we’re exposed to extreme heat, our hearts pump faster, circulating more blood through our body to cool us down as it would during exercise, said Dr Daniel Gagnon, a researcher at the Montreal Heart Institute in Canada who has also studied the potential cardiovascular impact of heat therapy. This could explain why regular sauna use has been tied to lower rates of cardiovascular calamities, he said, but scientists haven’t as yet definitively proven that saunas themselves can be protective.

“So far, we’re really missing the link to say, ‘Yes, for sure, it does something,’” he said. But the heart’s response to heat might mimic mild exercise, he said, perhaps like a light ride on a stationary bike.

“We know that the more you work a muscle, the better a shape it’s in, and the longer it lasts,” said Dr Rita Redberg, a cardiologist at the University of California, San Francisco, US.

People with heart conditions, such as angina or congestive heart failure, should speak to a doctor before going to a sauna, said Dr Melinda Ring, director of integrative medicine at Northwestern Medicine in the US. Pregnant women should also consult their physician. And if you’re already at a risk of getting dehydrated — for example, if you’re intoxicated — you should also steer clear of the sauna, she advised.

Some spa companies advertise the illusion of a sauna “detox” — the idea that sitting in the heat or steam can leach chemicals from your body. “There’s this image of ‘All the sweat is going to carry these toxins out’,” said Ring. “That’s really not how it works.” It’s not clear that sauna therapy can lower overall toxin loads in the body, she said.

Although some sauna companies claim that sweating can boost immunity, there isn’t robust evidence suggesting that a sauna, on its own, will make you more resistant to illness, Gagnon said. But saunas do reduce stress levels in some people, Kunutsor added, which can benefit the immune system.

And the idea that saunas can make someone magically shed pounds is also false, Lee said. But the most effective time to hop in a sauna may be after a workout, he added, as the heat may be able to amplify the cardiovascular perks of exercise.

He said the “jury’s out” on the long-term benefits of sauna use without exercise. And although saunas may help to make muscles more pliable, potentially alleviating aches, he said, there isn’t convincing evidence that a post-workout sweat can really prevent injuries, either.

As promising as some of the research around saunas is, he said, without more studies, it’s not totally clear which claims about the health perks saunas are accurate, and which are exaggerated.

“I do find a lot of hogwash — a lot of charlatans,” he said.

NYTNS