Prolonged sauna sessions may put bathers at risk of heat stroke, especially if they haven't consumed enough water beforehand, doctors have warned in the journal BMJ Case Reports. The warning comes after medical professionals treated a woman in her early 70s who required hospital admission following an extended sauna session at her local gym.

"Sauna use is a rare but potentially important cause of classical heat stroke," the doctors of a new case report warn.

Heat stroke is defined as a sharp increase in core body temperature above 40C that is associated with acutely impaired brain function.