Human thermoregulation in sauna.

Abstract

Finnish sauna is heated by the radiation energy of an electrical or wood burning stove resulting in high air temperature, 80-100 degrees C, and low air humidity levels, 50-60 g/kg of air. Sauna bathing is divided into several 5-20 min sessions and between the sessions several minutes are spent at normal room temperature. Finnish sauna presents a heat load of 300-600 W/m2 of skin surface area. This increases mean skin temperature to 40-41 degrees C, causes strong heat sensations and starts thermoregulatory mechanisms. Evaporative heat transfer by sweating is the only effective channel dissipating heat from the body in sauna. Sweating is usually 0.6-1 kg/h and represents a heat loss of about 200 W/m2. The body cannot compensate for the heat load of sauna and the temperature of viscera begins to increase. A 30-minute stay in a sauna with a temperature of 80 degrees C increases rectal temperature by about 0.9 degrees C in adults whereas in children less intensive sauna (10 min at 70 degrees C) increases rectal temperature by 1.5 degrees C. The subjective feelings after Finnish sauna are usually described in positive terms such as "calm" and "pleasant".