Saunas and cold plunges
Sauna has the stronger evidence of the two, but all of it is observational. In a Finnish study of 2,315 middle-aged men followed for a median of 20.7 years, those who used a sauna 4 to 7 times a week had about half the risk of fatal cardiovascular disease, and a 40% lower risk of death from any cause, compared with men who went once a week. That shows a link, not proof of cause: men who use a sauna most days may differ in other ways. The study looked at traditional Finnish saunas. We found no long-term outcome studies like it for infrared saunas or sauna blankets.
Laukkanen et al., JAMA Internal Medicine, 2015
Cold plunge has much weaker evidence. A 2025 review of 11 randomised trials (3,177 people) found that stress was lower 12 hours after cold-water immersion and that inflammation rose briefly straight afterwards, but the authors concluded that the claimed benefits "remain unsubstantiated". None of the trials measured long-term health or lifespan.
Not medical advice. Heat and cold both put real strain on the heart and blood pressure. If you have a heart condition, are pregnant, or take regular medication, talk to your doctor before using either.