Basking too long in a sauna without adequate hydration may risk heat stroke, doctors warn
Basking too long in a sauna may put bathers at risk of heat stroke, particularly if they haven't drunk enough water beforehand, warn doctors in the journal BMJ Case Reports, after treating a woman whose condition required admission to hospital.
Although relatively rare, heat stroke can be life threatening, even in the absence of various underlying risk factors, such as heart, lung, or neurological disease, and heavy drinking or taking a cocktail of prescription meds, they point out.
Heat stroke is defined as a sharp increase in core body temperature above 40°C that is associated with acutely impaired brain function, and ‘non-exertional’ heat stroke results from prolonged exposure to high environmental temperatures, explain the authors.
They treated a woman in her early 70s who had been found unconscious in her local gym’s sauna, where she had been doing stretching exercises for around 45 minutes.
Her core body temperature was 42°C-normal temperature is 36.4°C-her blood pressure was extremely low, and her heart rate was extremely high. She had a seizure after her arrival in emergency care.
She had previously been diagnosed with type 1 diabetes and an underactive thyroid, but she wasn’t a smoker or heavy drinker, and was a regular gym goer, so had few risk factors, point out the authors.
She was rapidly cooled with wet towels and a fan and given intravenous fluids and blood products to stabilise her.
Blood tests revealed malfunctioning kidneys and liver, evidence of a minor heart attack, and muscle tissue breakdown (rhabdomyolysis).
She regained consciousness within 2 hours of reaching normal core temperature but was confused and drowsy for 2 days. By day 3 this had resolved and she had no further seizures during her inpatient stay, which lasted 12 days.
After 26 days she had more or less fully recovered, except for some mild fatigue and mild liver function disturbance.
This is just one case report after prolonged sauna use, and as far as the authors are aware, only 9 other similar cases have been reported. But 3 of those people died as a result.
“The prognosis of heat stroke varies according to patient factors, particularly extremes of age,” explain the authors. “Classical heat stroke in elderly people carries a mortality rate of [more than] 50%, and this increases further with each additional organ dysfunction.
“Heat-related deaths spike during heat waves, as has been observed in multiple large international datasets. Deaths from heat stroke are expected to rise as global temperatures continue to increase," they add.
“Once heat stroke has occurred, the key determinate of outcome is how rapidly a patient is cooled, as the time spent with elevated core body temperature is correlated to the degree of cellular damage,” they emphasise.
The woman in question comments: “My experience has emphasised the dangers of saunas and how important it is to be fully hydrated on entering a sauna, and for them to be regularly checked by staff. As a regular sauna user, I never suffered any issues and, on reflection, I believe I had not drunk enough water.”
Reference:
McIver WJ, Zia MSevere heat stroke with multiorgan failure following collapse in a saunaBMJ Case Reports CP 2025;18:e262069.
