Finnish sauna vs infrared sauna: what the data show and how to use them sensibly

In Finland the sauna is part of everyday life, and in recent years it has also become a favourite biohacking tool. Alongside the traditional Finnish sauna, infrared saunas have become widespread; they heat the body differently and at a lower air temperature. Both have their place – but it helps to know what to expect from them and when to be careful.

What heat does to the body

In a Finnish sauna at around 80–100 °C with low humidity, the skin warms up quickly and core body temperature rises by a few tenths of a degree up to roughly one degree. The heart speeds up much as it does during light physical activity, blood vessels in the skin widen, and blood pressure often falls slightly during and shortly after the session. The body cools itself by sweating, losing both fluid and salts.

With repeated heat exposure the body gradually adapts: it starts sweating sooner, blood plasma volume increases and heat becomes easier to tolerate. This is well known from athletes acclimatising to hot environments, and small studies suggest that regular post-workout sauna sessions may contribute to it. In the laboratory, heat activates so-called heat shock proteins, which help cells cope with stress. How much this contributes to human health is not yet known.

The Finnish studies: association, not proof

The most frequently cited data come from a Finnish cohort study that followed more than two thousand middle-aged men from eastern Finland for about two decades. Men who used the sauna four to seven times a week had a lower risk of sudden cardiac death, death from cardiovascular disease and death from any cause than those who went once a week. Similar associations were later described in the same data for high blood pressure and dementia.

These are, however, observational data. People who take a sauna almost every day may already be healthier, have more free time, better social support or a different lifestyle. The researchers tried to account for these factors, but they cannot be ruled out entirely. The study also mainly included men from a single country with a traditional Finnish sauna. The results are interesting and consistent, but they do not prove that the sauna itself extends life.

Recovery and sleep

Many people say they feel relaxed and sleep better after a sauna. For sleep there is indirect evidence: according to a pooled analysis of studies, a warm bath or shower one to two hours before bed shortens the time it takes to fall asleep, probably because a warmed body then sheds heat faster and core temperature drops. Direct studies with saunas are still small. For post-exercise recovery the results are mixed – a sauna may improve how you feel, but it is unclear whether it speeds up muscle repair.

How an infrared sauna differs

An infrared sauna does not mainly heat the air; it emits infrared radiation that is absorbed by the skin and surface tissues. The air in the cabin is usually around 45–60 °C, which many people find more comfortable, especially those who tolerate the hot air of a Finnish sauna poorly. Body temperature rises more slowly, so sessions tend to be longer.

Research on infrared saunas is much more limited. Small studies of gentle repeated heating in heart failure, carried out under medical supervision, suggest improvements in some measures, but the groups were small and the conditions clinical. The Finnish cohort data concern traditional saunas and cannot simply be transferred to infrared ones. The claim that an infrared sauna “sweats out toxins” more effectively is unfounded: sweat is mostly water and salts, and waste removal is handled by the liver and kidneys.

Who should be cautious

• People who have been drinking alcohol – alcohol increases the risk of a drop in blood pressure, heart rhythm disturbances, overheating and injury. Do not combine it with a sauna.
• People with heart disease – a sauna is not recommended with unstable angina, shortly after a heart attack, with severe aortic valve stenosis or untreated rhythm disorders; if your condition is stable, talk to a cardiologist first.
• People with low blood pressure or a tendency to faint – there is a risk of dizziness when standing up and leaving the sauna; get up slowly and sit down first.
• People taking medication that affects blood pressure, heart rhythm or sweating – do not change your treatment, but ask your doctor whether and how you can use a sauna.
• Pregnant women – overheating, especially in the first trimester, is linked to a higher risk of birth defects; discuss sauna use with your doctor.
• Children – they regulate body temperature less well; if they use a sauna, it should be for shorter periods, at a lower temperature and always with adult supervision.
• People with a fever or acute illness – wait until you have recovered.
• Men trying to conceive – frequent heating can temporarily reduce sperm quality.

A practical protocol

• Drink before and after – a glass or two of water before the sauna and steady fluid replacement afterwards; for longer sessions, think about salts too.
• Finnish sauna – start with 5–10 minutes, later about 10–15 minutes at 80–90 °C, for one to three rounds.
• Infrared sauna – usually 15–30 minutes at 45–60 °C; keep the first sessions shorter.
• Cooling down – after each round, cool off with a lukewarm or cold shower and rest. A sudden plunge into ice-cold water is not suitable for people with heart disease.
• Frequency – two to four times a week is a sensible start for most people.
• Timing – if you want to support sleep, take your sauna one to two hours before bed, not right before.
• Listen to your body – leave the sauna immediately if you feel dizzy, nauseous, have chest pain or palpitations.
• Buying a home infrared sauna – look for CE marking, installation according to electrical standards and clear information on temperature and power. Treat promises of “detox” or “burning hundreds of calories” as a red flag.

Conclusion

The Finnish sauna is backed by interesting, if observational, data and is safe for healthy adults when used sensibly. The infrared sauna is a gentler alternative whose effects have been studied less. Use the sauna sober, drink enough fluids and build up gradually. If you have heart disease or low blood pressure, or if you are pregnant, talk to your doctor first. See the sauna as a pleasant part of a healthy lifestyle, not a substitute for one.