Short read
Joy Hussain and Marc Cohen of RMIT University in Melbourne ran a systematic review following Cochrane criteria, published open access in Evidence-Based Complementary and Alternative Medicine in 2018. They searched medical databases for studies from the year 2000 onwards that tested repeated dry sauna sessions in humans. They included 40 clinical studies with a total of 3,855 participants and formally assessed each for risk of bias.
Most of the included studies reported favourable effects, but the endpoints varied widely, which makes a pooled statement difficult. As an adverse effect, one small study with 10 participants reported disrupted sperm production that reversed after sauna use stopped. The review has no comparison group of its own; its findings summarise the individual trials.
The authors state explicitly that the effects promoted by providers are not adequately supported: detox, a raised metabolism, weight loss, better immune function and better sleep. The claim that a sauna detoxifies the body is therefore not backed by this body of evidence. Data on how often side effects occur and how severe they are are largely missing, as is information on the optimal dose and on which groups benefit most.
That makes this review the corrective in the collection. It confirms a generally positive direction and, in the same breath, marks where the evidence ends. It is the reason heatdive does not use the word detox as a claim, and it gives no basis for a recommended dose.