Sauna facilities are experiencing renewed interest as temperatures rise across parts of western Europe, which experienced its hottest June on record. The UK Health Security Agency has issued heat health alerts across much of England following the country’s fourth heatwave of the year. While sauna bookings initially declined as summer temperatures soared, operators report bookings have recovered, particularly at outdoor facilities offering both saunas and cold plunges.
Researchers are investigating whether repeated heat exposure through sauna use or hot water immersion could improve the body’s ability to tolerate heat. Prof Jari Laukkanen, a cardiologist at the University of Eastern Finland, notes that heat adaptation is well-established in sports physiology, with athletes using deliberate heat exposure to build tolerance. Similar adaptations may occur through passive heat exposure such as sauna bathing. Documented physiological changes include earlier and more efficient sweating, improved skin blood flow, expanded plasma volume, and reduced cardiovascular strain during subsequent heat exposure. Dr Jessica Mee of the University of Worcester is recruiting study participants to examine whether regular hot water immersion improves heat response.
However, experts caution that heat acclimation benefits may not apply universally and depend on the body’s capacity to increase sweating and skin blood flow. Effective heat training requires 40–60 minutes of daily exposure for at least four to six days, with benefits lasting approximately a week, though longer training produces longer-lasting effects. Certain individuals, including those with acute illness, fever, unstable angina, recent heart attacks, or uncontrolled low blood pressure, should avoid such exposure until medically assessed.
Experts strongly advise against using saunas during active heatwaves. Dr Mee emphasizes that heat acclimation is a preparatory strategy for milder months rather than a coping strategy during extreme heat events. Using saunas during peak heat may stack thermal challenges onto bodies already stressed by poor sleep, dehydration, and cardiovascular strain—conditions that increase heat-related illness risk. Additionally, most research occurs in supervised laboratory settings with controlled conditions, whereas unsupervised home use presents unknown safety profiles and fainting risks.
Researchers stress that heat adaptation does not substitute for established heat safety practices. Public health guidance—including staying hydrated, avoiding strenuous activity during peak heat hours, and monitoring vulnerable individuals—remains the most important protective approach during heatwaves.
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