Sauna is a form of passive heat therapy characterized by exposure to high ambient temperatures for short periods of time. It’s most heavily studied for its effects on the cardiorespiratory system, for which it can produce a number of benefits (many that are similar to exercise). The design and practices of saunas can vary considerably, which makes it difficult to directly compare studies on them.
Sauna is most often used for
Broadly, sauna is a form of passive heat therapy in which individuals sit in small, high-temperature rooms for short periods of time. The specific design and practices of using the sauna vary considerably, but the majority of research has been on traditional Finnish sauna, which is characterized by:
- Rooms made of wood and heated by hot rocks
- Temperature and humidity ranges of 90–100°C (170–212℉) and 10%–20%, respectively
- Durations of 5–20 minutes, although some go longer
- Cooling-off periods in which bathers swim, shower, or roll in snow
- A frequency of 1–3 times each week
The majority of sauna research focuses on its effects in people with cardiovascular disease. Acutely, sauna can lower blood pressure and improve measures of endothelial function and arterial stiffness (e.g., flow-mediated dilation and pulse-wave velocity). Over long durations, higher frequencies of sauna use have also been associated with 40%–70% reductions in the risk of all-cause mortality, cardiovascular mortality, hypertension and stroke.  Additionally, sauna may also benefit other conditions, such as dementia/Alzheimer’s disease, respiratory diseases, musculoskeletal disorders (e.g., arthritis), skin diseases, headache, and mental health disorders.
It’s been proposed that sauna may be a strategy for increasing healthspan and lifespan. There is compelling observational research to support this, in addition to mechanistic/non-human/uncontrolled trials on the subject, but direct, high-quality, well-controlled trials in humans are still somewhat lacking.
Although people with cardiovascular conditions were previously discouraged from using sauna, it’s accepted that sauna is safe (and likely beneficial) for people with stable cardiovascular disease. People with symptomatic, unstable, or unmanaged cardiovascular issues, such as unstable coronary artery disease, severe aortic stenosis, or recent myocardial infarction shouldn’t use sauna, however, because the physiological stress of sauna might precipitate a cardiac event. 
One of the biggest risk factors for adverse effects in the sauna is concurrent alcohol use: it both increases the risk of environmental injury (e.g., trauma from falling or heat injury from remaining in the sauna for too long) and can lower blood pressure to unsafe levels (sauna already has blood-pressure-lowering effects).
A few papers have raised concerns about sauna use during pregnancy, but the practice is considered safe and is common in Finland.
Overall, it’s worth appreciating that sauna is a low-risk but physiologically stressful activity. Individuals engaging in this practice should pay attention to how they feel and exit the sauna if they feel too uncomfortable.
Broadly, sauna seems to confer its benefits through the effects of heat on the cardiorespiratory, musculoskeletal, and integumentary (skin, hair, and nails) systems, among others. More specifically, sauna has been shown to reduce oxidative stress and inflammation, modulate immune and autonomic nervous system activity, and improve blood lipid and hormone levels. One especially noteworthy characteristic of sauna is its role as a “hormetic stressor”: it puts a mild stress on the body, which provokes cellular processes that encourage repair and protection from future stressors (a phenomenon known as hormesis). Exercise is another form of hormetic stressor, and indeed, sauna and exercise have very similar (but not identical) physiological effects, which include an increase in heart rate (120–150 beats per minute) and an elevation in skin and skeletal muscle blood flow, among others.
It’s worth remembering that, alongside its physiological effects, sauna is also simply a relaxing and pleasurable activity (with cultural significance for many); engaging in such activities is likely to benefit health in its own right.
- Bastu (Swedish)
- Banya (Russian)
- Saun (Estonian)
- Shvitz (Hebrew)
- Hammam (Turkish)
- Infrared therapy
- Waon therapy