New Study Exposes Life-Threatening Risks of Prolonged Sauna Use

Saunas can offer relaxation, but spending too long inside without proper hydration can lead to heat stroke, doctors warn.

While rare, heat stroke can become life-threatening even in healthy individuals without underlying conditions. This risk highlights the importance of staying hydrated and mindful of time spent in high-heat environments.

Sauna Safety Risks

Spending too much time in a sauna, especially without proper hydration, can increase the risk of heat stroke, warn doctors in BMJ Case Reports. Their warning follows the treatment of a woman whose condition became so severe it required hospitalization.

While heat stroke is relatively rare, it can be life-threatening even in people without common risk factors like heart, lung, or neurological diseases, heavy alcohol use, or the combined effects of multiple prescription medications, the doctors note.

Heat stroke occurs when the core body temperature rises sharply above 40°C (104°F), leading to impaired brain function. The authors explain that “non-exertional” heat stroke happens after prolonged exposure to high environmental temperatures, such as in a sauna.

Case Study: Severe Heat Stroke in a Sauna

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 (107.6°F) — normal temperature is 36.4°C (97.5°F) — 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.

Medical Intervention and Recovery

She was rapidly cooled with wet towels and a fan and given intravenous fluids and blood products to stabilize 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.

Wider Implications and Prevention Strategies

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 emphasize.

The woman in question comments: “My experience has emphasized 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: “Severe heat stroke with multiorgan failure following collapse in a sauna” by William Jack McIver and Muhammad Zia, 1 January 2025, BMJ Case Reports CP.
DOI: 10.1136/bcr-2024-262069

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