As the United Kingdom experiences its fourth heatwave of the year and western Europe records its hottest June on record, researchers are investigating whether repeated heat exposure through sauna use and hot water immersion could improve how human bodies cope with elevated temperatures.
Proponents of heat training point to established sports physiology principles showing that athletes deliberately use heat exposure to build tolerance before competing in hot environments. Prof Jari Laukkanen of the University of Eastern Finland notes that similar physiological adaptations may occur through passive heat exposure such as sauna bathing. These adaptations 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 conducting research on whether regular hot water immersion improves the body’s heat response, and notes that people accustomed to heat tend to pace themselves more sensibly, hydrate consistently and recognize warning signs earlier.
However, medical experts caution that heat training benefits may not apply equally to all populations and carry risks for certain individuals. People with acute illness, fever, unstable angina, recent heart attacks or uncontrolled low blood pressure should avoid such exposure until medically cleared. Additionally, effective heat training typically requires 40–60 minutes of heat exposure daily for at least four to six days, with benefits lasting approximately a week.
Experts emphasize a critical distinction: heat adaptation developed through regular training differs from acute heat protection. Laukkanen states there is currently limited evidence that using a sauna during an active heatwave protects people from heat-related illness. Mee warns that using saunas during extreme heat creates additional thermal stress on bodies already dealing with poor sleep, dehydration and cumulative cardiovascular strain, potentially increasing heat illness risk. She also notes that current research occurs in controlled laboratory settings with monitoring and supervision, and effects of unsupervised home use remain unknown.
Both researchers recommend that heat training occur during milder months as a preparation strategy rather than during peak heat events, and stress that public health measures including hydration, avoiding strenuous activity during the hottest hours and protecting vulnerable populations remain the most critical protective strategies.
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