As heatwaves grip much of Europe again this summer, scientists are examining a counterintuitive question: could deliberately sitting in a hot sauna help the body cope better when the mercury climbs outside? A growing body of research suggests the answer may be yes, though experts stress the benefit comes from repeated, gradual exposure over days or weeks, not a single trip to the sauna during a dangerous heatwave.
The UK Health Security Agency has issued heat health alerts across large parts of England as the country experiences its fourth heatwave of the year, according to The Guardian. The alerts follow a summer of extremes: the World Meteorological Organization has confirmed that western Europe recorded its hottest June on record, with average temperatures 3.05C above the 1991-2020 norm. Reuters has reported that the late-June heat was linked to more than 10,000 excess deaths across the continent, concentrated in France, Spain, Belgium and Germany.
Training the body for heat
The science behind the trend is heat acclimation, a well-established physiological process in which the body adapts to repeated heat exposure by sweating more efficiently, expanding blood plasma volume and lowering resting heart rate and core temperature. Jari Laukkanen, a cardiologist at the University of Eastern Finland who has researched the health effects of sauna bathing, told the Guardian that the body can become better able to handle later heat exposure when it is repeatedly exposed to heat over time.
Studies cited in the reporting suggest heat training typically requires 40 to 60 minutes of heat exposure daily for at least four to six days, with the resulting adaptations lasting around a week, though longer training programmes produce longer-lasting effects. This mirrors protocols long used by athletes and endurance sports scientists, who have studied sauna-based heat acclimation in runners and cross-country skiers preparing to compete in hot conditions.
“"There is currently limited evidence that going to a sauna during a heatwave itself protects people from heat-related illness or other conditions," said Prof Laukkanen.”
A booking rebound, and a caveat
The renewed scientific interest coincides with a shift in consumer behaviour. Nicola Pegues, head of operations at the not-for-profit Community Sauna Baths, which runs outdoor sauna and cold-plunge sites, said bookings initially fell as temperatures rose this summer but have since recovered. "But now we're seeing bookings come back," she said, adding that cycling between hot saunas and cold plunges offers people relief from the heat outside.
Some commercial saunas have begun marketing themselves as a way to prepare for or cope with extreme heat, a claim researchers say oversimplifies the evidence. Dr Jessica Mee of the University of Worcester, who is recruiting participants for a study on hot water immersion and heat response, noted that becoming accustomed to heat may change behaviour as much as physiology. People who are regularly exposed to heat tend to pace themselves more carefully, drink more water and notice warning signs of heat illness sooner, according to Mee, though she cautioned that these adaptations do not develop equally in everyone.
Whether sauna use makes sense during an actual heatwave depends heavily on individual circumstances, including underlying fitness, cardiovascular health and how closely a session is monitored. Public health authorities across Europe, including the UKHSA, continue to advise that during active heat alerts people should focus on staying cool, hydrated and out of direct sun, rather than seeking additional heat exposure.
For now, researchers frame heat acclimation as a long-term conditioning tool rather than an emergency remedy. The distinction matters as heatwaves become more frequent and intense across Europe: building tolerance in advance, through structured heat training, is a different proposition from trying to protect oneself once a dangerous heatwave has already arrived.
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