Sauna Research Standards are being developed internationally for the first time to help scientists use consistent definitions for sauna, heat therapy and different forms of passive heating. At the first International Heat Therapy Research Symposium held in Oslo in late September, researchers from nine countries began a Delphi consensus process. Its goal is to establish common terminology, methodological requirements and more precise standards for reporting temperature, humidity, session duration and other important parameters.
Research into the effects of sauna on the human body has expanded considerably in recent years. However, this growing interest has also revealed an important problem – different researchers do not always mean the same thing when they use terms such as “heat therapy” or even “sauna”.
One study may use a traditional Finnish sauna, another an infrared sauna, while a third may heat participants in hot water. Temperature, humidity, session duration, frequency and even the way these parameters are reported can differ considerably.
As a result, two studies may appear to investigate the same subject while their findings cannot be compared reliably.
This is precisely the problem the Sauna Research Foundation is now attempting to address.
Sauna Research Standards begin with a common language
From 22 to 24 September, the first International Heat Therapy Research Symposium was held at The Well in Oslo. It was not simply a meeting of researchers but also the beginning of a structured international Delphi process.
The working group involves 21 researchers from 14 institutions across nine countries. Fifteen researchers attended the Oslo meeting in person.
Universities and research institutions from the United States, Canada, the United Kingdom, Sweden, Norway, Finland, the Netherlands, Switzerland and New Zealand are represented.
The central task appears straightforward – researchers studying the same type of heat exposure should use the same terminology and describe it according to comparable principles.
What exactly is a sauna in scientific research?
In everyday life, the answer may seem obvious. In scientific research, the situation is considerably more complicated.
A traditional sauna with heated stones and water thrown onto them is not physiologically identical to an infrared cabin. Likewise, immersion in hot water heats the body differently from exposure to hot air.
Nevertheless, all these methods can appear in research examining passive heating or heat therapy.
One objective of the new initiative is therefore to establish standardised terminology for different methods – sauna, infrared heating, hot-water immersion, hammam, balneotherapy and other forms of heat exposure.
This would make it much clearer what a particular study has actually investigated.
Temperature alone is not enough
In a sauna study, it is not sufficient to report that participants spent time in a sauna at 80°C.
Air humidity, session duration, heating method, frequency of exposure and the overall study period are also important. It may also matter whether the temperature remained constant throughout the session and how the participant’s body temperature changed.
At present, these parameters are not reported consistently across different studies.
The Sauna Research Foundation argues that a common methodological reporting framework is needed so that future studies clearly describe not only their final results but also the precise conditions under which those results were obtained.
Many studies still involve relatively few participants
Another challenge is the scale of existing research.
Citing a recent review of heat-therapy research, the Sauna Research Foundation notes that most published experimental studies involve fewer than 40 participants.
In addition, 42 percent of the analysed studies do not include a control group.
This does not automatically mean that their findings are invalid. However, small participant numbers and differences in methodology limit the strength of broader conclusions.
If multiple smaller studies followed comparable standards, their results could later be combined in meta-analyses, potentially producing much stronger evidence.
Why are current findings difficult to compare?
Imagine two studies examining the effects of sauna on blood pressure.
In one, participants spend 15 minutes in an 80°C dry sauna three times a week. In another, participants spend 30 minutes at a lower temperature and different humidity level five times a week.
Both studies may have “sauna effects” in their titles, but the actual heat exposure received by participants can be substantially different.
If these differences are not described precisely enough, comparing the results becomes problematic.
The new standards are intended to establish a minimum set of information that researchers should report so that other scientists can understand and reproduce an experiment.
The Delphi method helps researchers reach consensus
The process launched in Oslo uses the Delphi method.
It is a structured method for developing expert consensus. Specialists assess specific statements over several rounds and, after each round, receive summarised information about the assessments of the wider expert group.
The objective is not to force agreement during a single discussion.
Experts can reconsider their assessments after reviewing the broader arguments and perspectives of other specialists. The process continues until a predetermined level of consensus is achieved.
For this project, consensus will require support from at least 80 percent of participating experts for a particular statement.
Oslo was only the first round
The three-day meeting in Norway represented the first round of the Delphi process.
Researchers worked on a working definition of heat therapy, a terminology glossary, a methodological checklist and the identification of important priorities for future research.
The process does not end there.
The resulting statements will be submitted to an external panel expected to include approximately 30–40 researchers and clinicians from North America, Europe and the Asia-Pacific region.
They will assess the statements over several rounds until it becomes clear which issues have achieved sufficient agreement within the international research community.
Final results are expected in 2027
The Delphi process is expected to conclude in 2027.
The final result is intended to be a peer-reviewed scientific publication containing agreed definitions, terminology, methodological priorities and research questions.
If successful, it could become an important reference point for future sauna and heat-therapy research.
This would matter not only to researchers themselves. Common standards could help scientific journals evaluate submitted studies, funding organisations assess research proposals and developers of clinical guidelines judge the quality of available evidence.
Sauna, infrared heat and hot water are not the same thing
One of the most important tasks of the proposed system will be to clearly distinguish between different heating methods.
If results from traditional sauna, infrared cabins and hot-water immersion are placed in the same category, conclusions can become overly simplified.
All these methods can increase body temperature, but heat transfer and the body’s physiological responses may differ.
Future studies therefore need to specify not simply that “heat therapy” was used, but exactly which method was applied and under what conditions.
Common standards do not mean identical saunas
The purpose of the initiative is not to establish one “scientifically correct” sauna temperature or decide what a real sauna should look like.
The issue is research quality.
Finnish sauna, smoke sauna, infrared sauna and other forms of heat exposure can be very different. That is precisely why researchers need to identify and describe them accurately.
The better the initial conditions are defined, the more reliably the results can be interpreted.
Sauna research is entering its next stage
Growing interest in the possible effects of sauna on cardiovascular health, metabolism, mental health, recovery and other areas has substantially increased the number of studies published in recent years.
But more publications do not automatically mean better knowledge.
If researchers use different definitions and methodologies, the scientific picture can become more complicated rather than clearer.
For that reason, the work begun in Oslo may attract less attention than another headline-grabbing study about a potential sauna benefit, but in the long term it could prove considerably more important.
Sauna Research Standards could give scientists something the field has so far lacked – a common language. If researchers define sauna consistently and accurately report temperature, humidity, session duration and the type of heat exposure, studies from different countries can be compared much more reliably. Only then will it become easier to distinguish what science genuinely demonstrates about sauna from what, for now, remains an assumption.
Sources
Sauna Research Foundation – 2026 Initiatives: 1st International Heat Therapy Research Symposium.
Sauna Research Foundation – International Researchers Convene in Oslo to Set the First Consensus Standards for Heat Therapy Research.
International Sauna Congress 2026 – The Future of Sauna Research.
