Finnish Sauna Health Benefits: New Research on the Role of Humidity

For generations, Finns have known that löyly changes the sauna experience. Now science is beginning to show that it changes the body’s physiological response too.

Löyly is created when water is thrown onto the hot stones of a sauna heater. The water evaporates rapidly, temporarily increasing the humidity and changing the way the heat feels on the body. But to Finns, löyly is much more than steam. It is an essential part of the sauna experience.

A new 2026 study by researchers from the University of Jyväskylä and the Finnish Institute of High Performance Sport KIHU provides new insight into what actually happens when humidity changes during Finnish sauna bathing. The researchers found that temperature and humidity both influenced the body’s physiological response, with humidity contributing independently to cardiovascular and thermoregulatory strain.¹

This is particularly interesting because scientific discussion around sauna has traditionally focused largely on temperature and time. Humidity, and especially the rapid changes created by löyly, has received considerably less attention.

So what does this new research tell us? And when we talk about the widely reported health benefits of sauna, what kind of sauna was actually studied?

What the new Finnish sauna study found

The study examined 50 healthy, recreationally active adults during four separate 10-minute sauna sessions. During the first two minutes of each session, no water was thrown onto the stones. For the remaining eight minutes, participants were free to create löyly by throwing water onto the heated stones.¹

The researchers measured the sauna environment in detail as well as participants’ heart rate, core body temperature, skin temperature and thermal sensations. Across the sessions, heart rate increased on average from approximately 79 to 121 beats per minute, while core body temperature rose by approximately 0.4°C.¹

Temperature was the dominant environmental factor, as might be expected. Importantly, however, humidity had an independent effect too. As the researchers conclude:

“While temperature is the dominant factor, humidity independently increases cardiovascular and thermoregulatory strain by impairing evaporative heat loss.”¹

In other words, löyly does not simply make the sauna feel different. The resulting change in humidity affects how the body responds to the heat.

The paper also raises an interesting issue concerning earlier research. Traditional sauna studies have often reported conditions as “dry”, even though water is customarily thrown onto the stones in Finnish sauna bathing. The rapid and temporary fluctuations caused by löyly have rarely been characterized in detail. The authors therefore suggest that previous studies may have underestimated the physiological strain associated with real-world sauna use.¹

This does not mean that the new findings prove löyly to be responsible for the long-term health benefits associated with sauna bathing. The study examined acute physiological responses, not long-term health outcomes. Much more research is needed to understand how humidity and löyly may relate to those outcomes.

But it does tell us something important: when studying Finnish sauna, humidity matters.

What are the health benefits of Finnish sauna?

Interest in the health effects of sauna has grown significantly in recent years, with new research continuing to add to the evidence. Some of the most influential long-term findings come from Finland.

One of the landmark studies was published in JAMA Internal Medicine in 2015. Laukkanen and colleagues followed 2,315 middle-aged men in Eastern Finland for a median of 20.7 years. More frequent sauna bathing was associated with a lower risk of sudden cardiac death, fatal coronary heart disease, fatal cardiovascular disease and all-cause mortality. Men reporting four to seven sessions per week had a 63% lower relative risk of sudden cardiac death and a 40% lower relative risk of all-cause mortality compared with those reporting one session per week.²

These are striking findings, but the wording matters. This was an observational study. It found associations and cannot establish that sauna bathing itself caused the lower mortality.

Other Finnish studies have reported similarly interesting associations. Frequent sauna bathing has been linked to a lower risk of dementia and Alzheimer’s disease³ and a reduced risk of developing hypertension.⁴ Reviews of the available evidence have also explored possible cardiovascular, respiratory, neurocognitive and other health effects.⁵

The picture extends beyond mortality and cardiovascular health. A 2024 population study from northern Sweden found that sauna bathers reported better general and mental health, greater happiness and energy, more satisfying sleep and less physical pain than non-sauna bathers.⁶ Most used electrically heated saunas, with typical bathing temperatures of 60–80°C. Again, this was a cross-sectional observational study, so the findings should not be interpreted as proof that sauna caused those differences.

Taken together, the evidence is promising. It gives us good reason to continue investigating the potential relationship between sauna bathing and cardiovascular health, blood pressure, cognitive health, sleep, mental wellbeing and overall wellbeing.

But it also raises an important question that is sometimes overlooked: when we say “sauna”, are we always talking about the same thing?

Why the type of sauna matters when discussing health benefits

In Finland, we do not normally call it a “Finnish sauna”. We simply call it sauna. And from our perspective, there should be little need for the prefix elsewhere either. Sauna is sauna. The reality, however, is that the word is increasingly used internationally for very different forms of heat exposure. This distinction becomes particularly important when health benefits are discussed. If different products and heat modalities are all called “sauna”, consumers should at least be able to understand what kind of sauna or heat exposure the scientific evidence behind a health claim actually relates to.

A traditional Finnish sauna exposes the body to relatively high air temperatures. It has a heater with hot stones, and water is thrown onto them to create löyly, producing rapid changes in humidity. Other forms of passive heat exposure can use different temperatures, heat sources, moisture levels and exposure times. The physiological stimulus is therefore not necessarily the same.

This distinction is particularly important when interpreting scientific evidence. A study can only provide direct evidence about the conditions and population that were actually examined. Findings from one form of heat exposure should not automatically be transferred to another simply because both are described using the word “sauna”.

The new Finnish research adds another dimension to this question. If humidity independently affects cardiovascular and thermoregulatory responses, describing sauna exposure only by temperature and duration may leave out an important part of the physiological picture.¹ Knowing whether water was thrown onto the stones, how moisture levels changed and what kind of sauna was used can matter when comparing studies and interpreting their results.

Do Finnish sauna health benefits apply to infrared and other heat therapies?

Infrared thermal exposure, often marketed as an “infrared sauna”, is frequently promoted with claims relating to cardiovascular health, recovery, longevity and other potential health benefits.

There is scientific research into infrared heat exposure, and it may have benefits of its own. The point is not that one heat modality is necessarily healthier than another. The important point is that they are not scientifically interchangeable.

Much of the widely cited long-term evidence discussed above concerns Finnish sauna bathing, not infrared thermal exposure. Scientific reviews of passive heat modalities also distinguish Finnish sauna from infrared thermal exposure and other heat-based interventions rather than treating them as a single modality. A comprehensive 2024 review by Laukkanen and Kunutsor describes Finnish sauna as the most commonly used and widely studied of these passive heat modalities and notes that it has the most consistent and robust evidence regarding health benefits to date.⁷

It is therefore important to be careful when health claims are made. Findings from studies of Finnish sauna bathing should not automatically be presented as evidence that infrared thermal exposure or other forms of passive heat exposure, such as products marketed as “sauna blankets” or “sauna capsules”, provide the same benefits simply because they are marketed using the word “sauna”.

Infrared thermal exposure should be evaluated on the scientific evidence relating to that method. Finnish sauna should be evaluated on research relating to Finnish sauna. That is not a criticism of either. It is simply how scientific evidence should be used.

Why Finnish sauna is not a dry sauna

Finnish sauna is often described internationally as a “dry sauna”. You may even have visited a hotel, gym or spa with a sauna carrying a sign saying, “Do not throw water on the stones.” From a Finnish perspective, there is something rather contradictory about that.

Löyly is an essential part of Finnish sauna bathing. Water is thrown onto the hot stones, where it evaporates rapidly and temporarily increases the humidity. This changes both how the heat is experienced and, as the new research demonstrates, how the body responds physiologically.¹ Without the possibility of throwing water onto the stones and enjoying löyly, most Finns would probably hesitate to call the experience a sauna at all.

Interestingly, the 2026 study addresses the “dry” description directly. Its authors point out that traditional sauna studies have often reported conditions as dry even though, in Finnish sauna, water is customarily poured onto the stones. They note that the resulting fluctuations in humidity have often been poorly characterized and that previous research may therefore have underestimated the physiological strain associated with real-world sauna use.¹

A Finnish sauna is not a steam room either. Humidity is not continuously high. It rises rapidly when water is thrown onto the stones and then falls again. The air may therefore be relatively dry between rounds of löyly, but Finnish sauna bathing itself is not simply dry heat.

For generations, Finns have known that löyly changes the sauna experience. Science is now beginning to show that it changes the body’s response as well.

More research is needed on Finnish sauna health benefits

The growing body of evidence around Finnish sauna and health is fascinating and, in many areas, highly promising. At the same time, there is still much we do not know.

We welcome much more research into Finnish sauna and its potential health benefits: larger and more diverse study populations, women as well as men, different age groups, and studies conducted in different countries and cultures. Further investigation into cardiovascular health, blood pressure, cognitive health, sleep, mental wellbeing and other potential effects would help build a broader and stronger evidence base. We would also welcome more work on the different elements of the Finnish sauna experience itself, including temperature, humidity and löyly.

More direct research comparing different passive heat modalities would also be valuable. In particular, studies comparing the physiological responses and potential health benefits of Finnish sauna bathing with infrared thermal exposure would help us better understand where the effects may be similar, where they differ, and whether findings from one modality can reasonably be applied to another.

Researchers themselves acknowledge the limitations of their studies, as good science requires. Some of the best-known long-term findings are based on observational studies and cannot establish cause and effect. Other important studies have involved relatively narrow populations, such as middle-aged Finnish men. The new findings on humidity provide an important piece of the puzzle, but the authors also call for further controlled research to isolate the independent effects of temperature and humidity.¹

Those of us working commercially in the sauna industry have a responsibility too. Scientific findings should be communicated accurately, together with their limitations. Good science acknowledges its limitations, and good communication should do the same. We should not turn associations into proven causal effects, nor should findings from Finnish sauna studies automatically become marketing claims for infrared thermal exposure or other forms of heat exposure that were not actually studied.

Science around sauna continues to develop, and we welcome that development. We hope researchers in Finland and around the world continue asking difficult questions, testing assumptions and building a broader evidence base. The more we learn about sauna, the better.

Finnish sauna is about more than health benefits

For centuries, we Finns have been going to sauna. For many of us, it begins in infancy and continues throughout our lives. Ask an average Finn why they go to sauna, however, and the answer is unlikely to begin with scientific studies or health statistics. We did not start going to sauna because studies told us to. We sauna because it has always been part of life.

Sauna has traditionally been a place for cleansing, but also for relaxation and recovery. It is a place to slow down and find balance, to spend time together and connect with others, or simply to be alone and present for a while. Sauna feels great and it makes us feel good.

And yes, the growing body of research suggests that Finnish sauna may be good for our health and wellbeing too. But perhaps part of the beauty of sauna is that we do not need to reduce it to a health hack, a performance metric or a promise of living longer. It is not something that needs to be optimised. The experience itself has value. Health and wellbeing are part of a much bigger whole.

That holistic sauna experience is what we at Hetki want to preserve and share with people around the world: authentic Finnish saunas where heat, hot stones, water and löyly belong together.

Because löyly is not an optional extra. It is an essential part of sauna.

Scientific references

1. Laatikainen-Raussi I, Mikkola T, Ihalainen JK, Ahokas E. Temperature and humidity independently influence thermoregulatory responses during Finnish sauna bathing. Temperature. 2026;13(3):289–299. doi:10.1080/23328940.2026.2698162.

2. Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Internal Medicine. 2015;175(4):542–548. doi:10.1001/jamainternmed.2014.8187.

3. Laukkanen T, Kunutsor S, Kauhanen J, Laukkanen JA. Sauna bathing is inversely associated with dementia and Alzheimer’s disease in middle-aged Finnish men. Age and Ageing. 2017;46(2):245–249. doi:10.1093/ageing/afw212.

4. Zaccardi F, Laukkanen T, Willeit P, Kunutsor SK, Kauhanen J, Laukkanen JA. Sauna bathing and incident hypertension: a prospective cohort study. American Journal of Hypertension. 2017;30(11):1120–1125. doi:10.1093/ajh/hpx102.

5. Laukkanen JA, Laukkanen T, Kunutsor SK. Cardiovascular and other health benefits of sauna bathing: a review of the evidence. Mayo Clinic Proceedings. 2018;93(8):1111–1121. doi:10.1016/j.mayocp.2018.04.008.

6. Engström Å, Hägglund H, Lee E, Wennberg M, Söderberg S, Andersson M. Sauna bathing in northern Sweden: results from the MONICA study 2022. International Journal of Circumpolar Health. 2024;83(1):2419698. doi:10.1080/22423982.2024.2419698.

7. Laukkanen JA, Kunutsor SK. The multifaceted benefits of passive heat therapies for extending the healthspan: a comprehensive review with a focus on Finnish sauna. Temperature. 2024;11(1):27–51. doi:10.1080/23328940.2023.2300623.