Hydrogen sulfide and the physiology of "totonou": a hypothesis on sauna-induced vascular recovery.

Sauna bathing, a traditional health practice in Finland and Japan, has been associated with reduced cardiovascular and neurological risks. Circulatory recovery, marked by a shift from sympathetic to parasympathetic dominance, underlies the relaxation state known as "totonou." Traditionally attributed to nitric oxide (NO), this effect may also involve hydrogen sulfide (H2S), a gaseous mediator with vasodilatory, antioxidant, and anti-inflammatory properties. We hypothesize that H2S facilitates sauna-induced circulatory recovery and that environmental exposure may modulate this process. This perspective highlights H2S as a novel regulator and calls for basic, clinical, and epidemiological studies to test this hypothesis.