Repeated use of saunas could help people cope better in heatwaves, scientists say

Even as summer temperatures soar, the sauna trend is booming, with some venues touting them as a way to beat the heat. But while experts have urged caution about sweating it out in hot weather, a growing number of studies are considering whether heat training could help people prepare for heatwaves.

With parts of the UK experiencing their fourth heatwave of the year, the UK Health Security Agency (UKHSA) has issued heat health alerts across much of England. The warnings follow an unprecedented summer, with western Europe experiencing its hottest June on record.

Nicola Pegues, head of operations at the not-for-profit Community Sauna Baths, said that initially bookings fell as temperatures rose. “But now we’re seeing bookings come back,” she said, adding all of the sites are outdoors with saunas and cold plunges, allowing people to cycle between the two. “You get real relief out of it actually,” she said.

Prof Jari Laukkanen, a cardiologist at the University of Eastern Finland who has carried out research into the health benefits of saunas, argues that repeated exposure to heat can help the body gradually become better at coping with heat exposure.

“This is well established in sports physiology, where athletes deliberately use repeated heat exposure to improve heat tolerance before competing in hot environments,” he said. “Indeed, quite similar physiological adaptations may also occur with passive heat exposure, such as sauna bathing and hot water immersion.”

Laukkanen noted heat adaptations include earlier and more efficient sweating, improved skin blood flow, expansion of plasma volume and reduced cardiovascular strain during subsequent heat exposure.

“In other words, regular heat exposure may help the body regulate temperature more efficiently,” he said.

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Dr Jessica Mee, of the University of Worcester, who is recruiting participants to study whether regular hot water immersion could improve how the body responds to heat, said regular heat exposure also changed how hot people felt and how they behaved.

“People who are accustomed to heat pace themselves more sensibly, hydrate more consistently and recognise their own warning signs earlier,” she said.

But heat acclimation may not benefit everyone equally. “The adaptations rely heavily on the body’s ability to increase sweating and skin blood flow,” said Dr Heather Massey, an expert in extreme environments and physiology at the University of Portsmouth.

There are also safety concerns around saunas and hot baths for people with an acute illness or fever, unstable angina, a recent heart attack, or uncontrolled low blood pressure, with Laukkanen noting that they should avoid such exposure until medically assessed or treated.

Experts add that heat training typically takes 40–60 minutes of heat exposure each day for at least four to six days, and that the benefits last for about a week – although longer training leads to longer-lasting effects.

But while some saunas are already advertising themselves as an unexpected solution to heatwaves, whether they are a good idea during a heatwave depends upon the context – such as the fitness of the individual and the level of monitoring.

Laukkanen stressed heat adaptation was not the same as heat protection. “There is currently limited evidence that going to a sauna during a heatwave itself protects people from heat-related illness or other conditions,” he said. “The benefits are more likely related to long-term adaptation through regular heat exposure rather than using a sauna as an acute treatment during very hot weather.”

Mee said: “Heat acclimation is a preparation strategy for the mild months, not a coping strategy for the hottest day of the year.”

Mee said one issue on a hot day was that there was no meaningful recovery when using a sauna or hot bath.

“You are stacking one thermal challenge on top of another, on a body that in all likelihood is already dealing with several consecutive nights of poor sleep, some degree of dehydration and cumulative cardiovascular strain,” she said. “That is precisely the profile in which heat-related illness develops.”

Another issue, said Mee, was that studies were carried out in a supervised laboratory or controlled settings, where temperature was monitored, exposure time was controlled and someone was present throughout.

“We do not yet know how safely or effectively this transfers to people doing [hot baths] unsupervised at home,” she said, adding the most immediate risk was fainting.

Laukkanen encourages following public health advice during a heatwave. “Regular heat exposure is not a substitute for staying hydrated, avoiding strenuous activity during the hottest part of the day, and looking after vulnerable people,” he said. “Those remain the most important measures.”