How healthy are saunas? And can they really simulate a workout without the work?

How healthy are saunas? Along with steam baths and sweat lodges, they’re baked into cultural traditions for people across the globe, from Scandinavians to Koreans to Native Americans. And saunas themselves come in different permutations – in Ireland we’re most used to the wood-lined Finnish-style saunas known for their dry heat; more modern infrared saunas often use light panels to generate heat; steam rooms fill with moist vapour.

As saunas become more trendy – some people are even installing them at home – 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, says Earric Lee, a researcher at the University of Jyväskylä, in Finland, who has studied their health effects. “It’s not like, ‘Oh, instead of going for my 45-minute run, I’m going to sit in the sauna for 45 minutes,’’' he says.

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).

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Still, the findings suggest that saunas may help improve cardiovascular function, says 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, generally speaking, short bouts of intense heat stress our heart in beneficial ways – and strengthen the cardiovascular system over time, Kunutsor says.

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, says Dr Daniel Gagnon, a researcher at the Montreal Heart Institute 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 says, but scientists haven’t definitively proved that saunas themselves can be protective.

“So far, we’re really missing the link to say, ‘Yes, for sure, it does something,’” he says. But the heart’s response to heat might mimic mild exercise, he says, 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,” says Dr Rita Redberg, a cardiologist at the University of California, San Francisco.

Though saunas may help make muscles more pliable, potentially alleviating aches, according to Earric Lee of the University of Jyväskylä, in Finland, there isn’t convincing evidence that a post-workout sweat can prevent injuries

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

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,’” says Ring. “That’s really not how it works.” It’s not clear that sauna therapy can lower overall toxin loads in the body, she says.

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 says. But saunas do reduce stress levels in some people, Kunutsor adds, which can benefit the immune system.

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

In 2019, Lee tested this with 48 people, split into three groups: a control group with a largely sedentary lifestyle, one that worked out three times each week and a third that exercised in addition to going to the sauna for 15 minutes afterward. After eight weeks, the groups that worked out saw expected improvements in cardiovascular fitness and decreased fat mass, Lee says, but those who went to the sauna saw higher cardiovascular fitness gains and lower blood pressure and cholesterol levels than those who only worked out.

He says 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 says, there isn’t convincing evidence that a post-workout sweat can prevent injuries, either.

As promising as some of the research around saunas is, he says, 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 says. – A longer version of this article originally appeared in The New York Times