Steam Room vs Sauna: What the Research Shows
Key insights
- A steam room and a sauna are not the same room at two settings of one dial. A traditional sauna runs at roughly 80 to 100 degrees with relative humidity in the low tens of per cent; a steam room runs at roughly 40 to 45 degrees with humidity close to saturation. The lower air temperature does not make it the gentler room.
- In the one controlled crossover that put the same ten men through both, at 91 degrees and 18 per cent humidity in the dry room against 59 degrees and 60.5 per cent in the steam room, the increases in rectal temperature and heart rate were larger in the steam bath by 38.8 and 21.2 per cent respectively 1.
- The same trial found the cumulative heat strain index roughly doubled in the steam room, 144.6 against 76.3, and the physiological strain index rose from 4.83 to 5.7, despite the air being more than 30 degrees cooler 1.
- The mechanism is evaporation. Near saturation, sweat cannot evaporate from the skin, so the body's principal cooling route is closed and heat accumulates faster even though the room feels less severe on entry 1.
- Almost every long-term outcome finding people cite for heat bathing was collected on dry Finnish sauna, not on steam: the 2,315-man cardiovascular mortality cohort followed for a median of 20.7 years, and the 1,935-man respiratory disease cohort followed for 25.6 years 2 3. No comparable cohort exists for steam rooms.
Most gyms put the two rooms next to each other, which quietly suggests they are interchangeable. They are not, and the intuition most people form on the way in is backwards. The sauna reads 90 degrees on the wall thermometer and the steam room reads about 43, so the steam room looks like the softer option and the sauna looks like the serious one.
Air temperature on its own is not a measure of thermal load. What determines how much heat ends up stored in the body is the balance between heat gained from the environment and heat the body can shed, and in a hot room almost all of that shedding is done by sweat evaporating off the skin. Humidity governs whether that can happen. A room at 43 degrees and near-total saturation removes the escape route; a room at 90 degrees and 15 per cent humidity leaves it wide open.
What follows is what happened when researchers measured both in the same subjects, why the long-term evidence base is so lopsided between the two, and what that should and should not mean when you are deciding which room to build.
Why the cooler room is the harder one
Evaporating a litre of sweat carries away roughly 2,400 kilojoules of heat. That is the body's dominant cooling mechanism once ambient temperature exceeds skin temperature, at which point radiation and convection stop helping and start adding heat instead. Evaporation depends on a vapour pressure gradient between wet skin and the surrounding air. As relative humidity approaches 100 per cent that gradient collapses. Sweat still forms, and it still runs, but running off the body does nothing thermally. It is the phase change that cools you, and in a steam room the phase change largely does not occur.
In a Finnish sauna the opposite holds. The air is extremely hot but very dry, so sweat evaporates almost as fast as it appears, and the evaporative cooling partially offsets the heat coming in from the stove and the walls. This is why an experienced bather can sit comfortably at 90 degrees for fifteen minutes but finds a room at half that temperature and full humidity unbearable within a few minutes. The subjective harshness and the physiological load are pointing in opposite directions.
What a direct comparison found
Pilch and colleagues ran the comparison properly. Ten healthy men aged 25 to 28, none of them habitual sauna users, completed a dry sauna protocol and then, after a one-month washout, a steam sauna protocol. Each session was three fifteen-minute exposures separated by five-minute breaks with a cold shower and seated rest. The dry room was held at 91 degrees and 18 per cent humidity; the steam room at 59 degrees and 60.5 per cent. Rectal temperature and heart rate were monitored throughout, blood pressure and body mass before and after, and both a physiological strain index and a cumulative heat strain index were calculated 1.
The steam bath was the more demanding exposure on every measure of thermal load. Rises in rectal temperature and heart rate were larger by 38.8 and 21.2 per cent, the physiological strain index rose from 4.83 to 5.7, and the cumulative heat strain index nearly doubled, from 76.3 to 144.6. Subjective heat discomfort was also greater in the steam room. Both protocols raised systolic blood pressure, though the rise was larger after the dry sauna, and both reduced diastolic pressure to a similar degree 1.
Two caveats belong with those numbers. The sample was ten men, and the steam room in the study was hotter than most commercial steam rooms, which typically sit nearer 43 degrees. The direction of the finding is nonetheless clear and mechanistically expected: at high humidity the body loses its ability to regulate, and thermal strain rises faster than the wall thermometer suggests.
Where the long-term evidence actually comes from
This is the part that gets lost when the two rooms are treated as equivalent. The health claims made for heat bathing rest overwhelmingly on Finnish cohort data, and Finnish cohorts studied Finnish saunas.
The Kuopio Ischaemic Heart Disease study followed 2,315 middle-aged men for a median of 20.7 years. Compared with one session a week, four to seven sessions a week were associated with a 48 per cent lower risk of fatal coronary heart disease and a 40 per cent lower risk of all-cause mortality, and sessions longer than 19 minutes with a 52 per cent lower risk of sudden cardiac death 2. A separate analysis of 1,935 men from the same cohort, followed for a median of 25.6 years, found hazard ratios for respiratory disease of 0.73 and 0.59 for two to three and four or more sessions weekly, with a similar pattern for pneumonia specifically 3.
There is no steam-room equivalent of either. A systematic review of regular dry sauna bathing identified 40 clinical studies covering 3,855 participants, of which only 13 were randomised controlled trials and most enrolled fewer than 40 people 4. If that is the state of the better-studied modality, the steam room is several steps further back. Acute work does show that heat bathing loads the cardiovascular system in a way that resembles moderate exercise, with blood pressure and heart rate climbing throughout the exposure and blood pressure settling below baseline afterwards 5, and there is no physiological reason that response would be absent in a steam room. But an acute mechanism is not an outcome, and no one has followed steam-room users for two decades.
Realistic expectations
The honest summary is narrower than either camp would like. A steam room is not a weaker sauna; measured by thermal strain it is arguably a stronger stimulus per minute, and that cuts both ways, because greater strain also means a shorter tolerable exposure and less margin for anyone with cardiovascular limitations. What the steam room lacks is not plausibility but longitudinal evidence. Absence of a cohort study is not evidence of absence of benefit, and it would be dishonest to present it as such.
Where steam has a defensible edge is the upper airway. Warm saturated air is the reason people reach for a steam room with a blocked nose, and the subjective relief is real even though it has not been shown to shorten an illness. Where the sauna has the edge is everything that depends on accumulating sessions over years, because that is the only exposure anyone has actually tracked over years.
Practical guidance
If you are choosing one room and want to reproduce the protocol behind the outcome data, that protocol is a traditional dry sauna, roughly 80 to 100 degrees, sessions of around 15 to 20 minutes, four to seven times a week 2. Do not translate steam-room time one-for-one into sauna time; because thermal strain accumulates faster in humid heat, a sensible steam session is shorter, and stacking multiple long rounds is where people get into difficulty. Rehydrate against measured body-mass loss rather than thirst in either room, and treat lightheadedness on standing as the signal to stop for the day rather than something to push through.
If the appeal of steam is the sensation rather than the outcome data, a traditional stove with a decent mass of stones gives you a large part of it. Ladling water over hot stones produces löyly, a transient humidity spike that raises perceived heat sharply for a minute or two, inside a room that otherwise stays dry enough to sweat efficiently. That is a different question from infrared, which we have covered separately in our comparison of infrared and traditional saunas.
The Contrast Market Perspective
The dose in this literature is defined by two numbers held together, temperature and humidity, and a room that cannot hold both reliably is not delivering the protocol the studies tested. That is a build question before it is a wellness question: heater sizing against room volume, stone mass, vapour barrier and ventilation are what determine whether a cabin actually sits where you set it, session after session, rather than drifting. Steam rooms are less forgiving still, since a sealed and correctly drained enclosure is the difference between a durable room and a maintenance problem. If you would like help deciding which room suits your space, climate and how you intend to use it, Schedule a consultation.
References
Footnotes
- Pilch W, Szygula Z, Palka T, Pilch P, Cison T, Wiecha S, Tota L (2014). Comparison of physiological reactions and physiological strain in healthy men under heat stress in dry and steam heat saunas. Biology of Sport. PubMed ↩︎
- Laukkanen T, Khan H, Zaccardi F, Laukkanen JA (2015). Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Internal Medicine. PubMed ↩︎
- Kunutsor SK, Laukkanen T, Laukkanen JA (2017). Sauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort study. European Journal of Epidemiology. PubMed ↩︎
- Hussain J, Cohen M (2018). Clinical effects of regular dry sauna bathing: a systematic review. Evidence-Based Complementary and Alternative Medicine. PubMed ↩︎
- Ketelhut S, Ketelhut RG (2019). The blood pressure and heart rate during sauna bath correspond to cardiac responses during submaximal dynamic exercise. Complementary Therapies in Medicine. PubMed ↩︎