Sauna

How sauna bathing affects your body

When you sit in a sauna at 80–100 °C, your core temperature rises by 1–2 °C within 15–20 minutes. This triggers a cascade of protective responses. The most important: your cells ramp up production of heat shock proteins (HSPs). HSP70 and HSP90 act as molecular repair crews, fixing misfolded proteins and shielding cells from stress damage. Repeated sessions can raise HSP70 levels by about 45% and HSP90 by 38% ^[1]. This is hormesis at work, the same type of beneficial stress response that makes exercise and fasting so effective.

Your heart rate climbs to 120–150 bpm during a session, roughly equivalent to a brisk walk or moderate cycling. Blood vessels dilate, blood pressure drops, and endothelial function improves over time. For people who can't exercise at full capacity, sauna offers many of the same cardiovascular training effects ^[4].

Cardiovascular and mortality benefits

The strongest evidence comes from the Finnish Kuopio Ischaemic Heart Disease Risk Factor (KIHD) study, which tracked over 2,300 men for 20 years. Men who used the sauna 4–7 times per week had a 63% lower risk of sudden cardiac death, 50% lower fatal cardiovascular disease risk, and 40% lower all-cause mortality compared to once-weekly users ^[1]. A follow-up study including women confirmed these dose-dependent benefits ^[3]. A 2024 study found that frequent sauna bathing may even counteract the harmful effects of elevated blood pressure on mortality risk ^[7].

The 2023 Mayo Clinic Proceedings review further showed that combining sauna with regular physical activity produces cardiovascular benefits beyond what either practice achieves alone ^[8].

Brain health and dementia prevention

In the same Finnish cohort, 4–7 weekly sauna sessions were linked to a 66% lower dementia risk and 65% lower Alzheimer's risk compared to once-weekly use ^[2]. These numbers held up after adjusting for age, alcohol, BMI, blood pressure, and chronic conditions. The likely mechanisms include increased BDNF production (which supports neuron growth and repair), improved cerebrovascular blood flow, and reduced neuroinflammation.

Respiratory health

Sauna bathing also benefits the lungs. In the KIHD cohort, men with 4+ weekly sessions had a 47% lower risk of pneumonia and a 37% lower risk of other respiratory diseases compared to those using the sauna once a week or less ^[9][10]. Heat exposure improves ventilation, increases vital capacity, and may reduce pulmonary congestion. A 2023 study also reported a lower risk of chronic obstructive pulmonary disease (COPD) among frequent sauna users ^[11].

Hormonal, metabolic, and mood effects

Sauna triggers a complex hormonal response. Growth hormone can spike up to 16-fold after repeated sessions. Norepinephrine rises by 100–310% depending on temperature, sharpening focus and alertness. Beta-endorphins increase substantially, producing the characteristic post-sauna sense of calm and well-being ^[6].

There's also a less obvious mood mechanism. During heat discomfort, your brain releases dynorphin, which temporarily feels unpleasant but sensitises mu-opioid receptors. After the session, normal endorphin levels hit harder, leaving you with an elevated baseline mood. This is why regular sauna users often describe it as mildly addictive.

Metabolic effects include improved insulin sensitivity through GLUT4 transporter activation and temporary elevation of white blood cell counts, supporting immune function. A 2024 UCSF study found that whole-body hyperthermia combined with cognitive-behavioral therapy produced significant reductions in depressive symptoms, with 11 of 12 participants no longer meeting criteria for major depression after treatment ^[12].

Finnish sauna vs. infrared sauna

Traditional Finnish saunas run at 80–100 °C with low humidity. Infrared saunas use wavelengths of 6–12 micrometres to heat tissue directly at lower air temperatures of 45–65 °C. Both raise core temperature effectively, but the long-term mortality data comes exclusively from traditional Finnish saunas ^[4]. Infrared saunas are better tolerated by people sensitive to extreme heat and show benefits for pain relief, muscle recovery, and relaxation in smaller studies. If you have access to a traditional sauna, that's the modality with the strongest evidence behind it.

Practical protocols

For the greatest health benefits, aim for 15–20 minutes per session at 80 °C or above, 4–7 times per week. Cold exposure after the sauna (a plunge at 4–10 °C or a cold shower) amplifies norepinephrine release and strengthens the hormetic effect. A single 20-minute session can produce 0.5–1 litre of sweat, so replace fluids and electrolytes (sodium, potassium, magnesium) before and after. Beginners should start with 5–10 minutes and build up gradually over several weeks.