Traditional sauna — Mixed and mostly low-certainty

Traditional sauna, often called Finnish or dry sauna, is a wood-lined room heated by an electric or wood-burning stove to roughly 80–100°C (175–212°F) at low relative humidity, typically 10–20%. Water ladled over hot stones (löyly) raises humidity in short bursts, which is why a "dry" sauna rarely stays dry throughout a round. This is the older and hotter counterpart to infrared sauna: the air itself is heated and warms you by convection, rather than infrared light warming the body directly at a lower ambient temperature. Studio formats vary, communal cedar or spruce cabins, private rentable rooms, and guided sauna-and-cold circuits that pair rounds with a plunge, cold shower, or rest period. Sessions are usually taken as several short rounds of 5–20 minutes separated by cooling and rehydration, rather than one long sit. In the US, traditional sauna is most often found inside bathhouses, Nordic-style spas, recovery lounges and full-service gyms rather than as a standalone storefront, and it is commonly bundled with contrast circuits. People use it as a heat-exposure and wind-down ritual; the research base is discussed below and is more mixed than the popular coverage suggests.

How traditional sauna works

Sauna heat drives a well-described acute physiological response: skin temperature rises toward about 40°C, heart rate increases, cardiac output rises roughly 60–70% with stroke volume broadly stable, and a large share of blood flow is redistributed from the core toward the skin. Blood pressure falls during exposure. Proposed longer-term mechanisms, heat-shock proteins, Nrf2 signalling, endothelial nitric-oxide effects, are described in review literature as plausible rather than demonstrated. The best-known human data come from a single long-running observational cohort of middle-aged Finnish men, in which more frequent sauna bathing was associated with lower rates of sudden cardiac death and of dementia over roughly two decades. Because participants chose their own sauna habits, that design cannot show cause: people well enough to sauna often are, by construction, a healthier group, and the findings have not been reproduced in an independent cohort. Controlled work is more sobering, a randomised crossover trial in healthy older adults found no significant change in flow-mediated dilation after one or two 10-minute sessions, so durable vascular adaptation is not established from single exposures. A 2018 systematic review concluded there is insufficient evidence to recommend any specific temperature, frequency, or duration for a specific health outcome.