Repeated Sauna Use Builds Heat Tolerance, Scientists Say
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- The UK Health Security Agency has issued heat health alerts across much of England as parts of the UK experience their fourth heatwave of the year, following western Europe's hottest June on record.
- Community Sauna Baths, a not-for-profit operator, says bookings initially fell as temperatures rose but have since rebounded; all its sites are outdoors and pair saunas with cold plunges for cycling between hot and cold.
- Prof Jari Laukkanen, a cardiologist at the University of Eastern Finland, says repeated heat exposure triggers adaptations including earlier and more efficient sweating, improved skin blood flow, expanded plasma volume and reduced cardiovascular strain — similar to those athletes develop through deliberate heat training.
- Dr Jessica Mee of the University of Worcester, who is recruiting participants for a study on regular hot water immersion, notes heat-acclimated people pace themselves more sensibly, hydrate more consistently and recognize their own warning signs earlier.
- Heat training protocols typically require 40–60 minutes of daily heat exposure for at least four to six days, with benefits lasting about a week, though longer training extends the effect.
- Dr Heather Massey of the University of Portsmouth cautioned the adaptations rely heavily on sweating and skin blood flow capacity, meaning benefits aren't equal for everyone, and people with acute illness, fever, unstable angina, a recent heart attack or uncontrolled low blood pressure should avoid saunas until medically cleared.
- Both Laukkanen and Mee stressed heat acclimation is not heat protection — Laukkanen said there is limited evidence a sauna during a heatwave itself prevents heat-related illness, while Mee called acclimation "a preparation strategy for the mild months, not a coping strategy for the hottest day of the year," with fainting flagged as the most immediate unsupervised risk.
Why it matters: The takeaway for consumers is timing: heat acclimation requires at least 4–6 days of 40–60 minute sessions, and benefits fade within about a week — so sporadic sauna visits offer little protection during an actual heatwave. Experts note venues are already marketing themselves as a heatwave fix, a claim that misrepresents the science.
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