Short read
Katriina Kukkonen-Harjula and Kirsi Kauppinen of the UKK Institute for Health Promotion Research in Tampere published this review of the health effects and risks of sauna bathing in the International Journal of Circumpolar Health in 2006, volume 65, issue 3, pages 195 to 205. Both authors have worked on sauna physiology for many years, in the country with the longest tradition of use. Kukkonen-Harjula later also co-authored a letter in Neurology on a sauna and stroke cohort study.
The review sorts the body's responses into two kinds: acute, passing reactions during and shortly after a session, and adaptations that develop with repeated exposure. It covers effects on circulation, the endocrine system and thermoregulation. As a review, it has no comparison group and reports no new figures of its own.
Published in 2006, it appeared before the large prospective cohort analyses. Its physiological section is still considered valid; its epidemiological section has been overtaken by later findings.
The distinction it draws matters for how sauna findings are reported. An acute reaction to a single session is not the same as an adaptation to repeated exposure, and the two are regularly blurred when findings are summarised. The review offers a framework for keeping those apart; it does not show which adaptations occur in any individual or how many sessions they would require.