Sauna Health

There are a number of proven physical and mental health benefits to sauna. As well as a number of myths. Here I’ll do my best to sort them all out.  

There is probably a lot more that we don’t know than that we do know. We’ve still a lot to learn.  This is exacerbated by definitional problems. There’s not a consistent definition of what a sauna is for instance. So one studies ‘sauna’ is not the same as another’s and then our ‘sauna’ not the same as either of those. With Trumpkin’s Taxonomy of Thermal Experiences and other efforts we will hopefully get to useable common definitions.

Note that folks in Finland and elsewhere quite consistently say that they don’t sauna for any health benefits. They sauna purely for enjoyment.

Note: In an effort to better organize and provide better edited information this is currently a cut & paste of health bits from various other posts. Hopefully it will improve considerably in the months to come.

Note II: If you spot any inaccurate information please let me know.

Disclaimer: I am not an engineer nor doctor. Nor any kind of expert on sauna. I’m a former and sometimes still researcher and journalist. 

 

Health – Cautions

Sauna is generally safe for all people of all ages. Many people in Finland begin going to sauna as a baby and continue for their entire lives. And, even temps as high as 140°c (284°f) appear completely safe (though recommended temps are 75-105°c).

If you have any concerns about going to sauna then you should talk to your GP. This particularly if you are overweight, obese, sedentary, pregnant or have any cardiovascular conditions or high blood pressure. It’s likely completely safe for you but some caution isn’t a bad idea.

Going to sauna places increased stress on our cardiovascular and other systems. This is good but can be risky for people who are not already fit. If you are overweight or sedentary then it might be good to incorporate some lifestyle changes such as moderate activity each day and eating more wisely before beginning a regular sauna routine. 

Cold Water vs Ears – Repeated or continued exposure of ears to cold water can lead to surfer’s ear, medically known as external auditory canal exostoses (EACE) or just exostoses. I’ve been unsuccessful in determining what dose is risky but know that it’s common among folks who swim, surf or dive (SCUBA, etc.) in colder water. Something to be cautious of. That said, if the water isn’t too cold then I’m a fan of full immersion – there’s really nothing like it that’s legal :-).

BE CAREFUL WHAT YOU BELIEVE – There are a lot of claims about this or that health benefit from sauna, cold plunging and other thermal bits. Some of these claims are true but many are not and based on junk science, lack of understanding of human physiology, or are outright lies to promote or sell saunas, IR booths, plunge pools and other things.

Viruses, Bacteria, Parasites and Fungi (mold) – Viruses, bacteria and fungi are either killed or inactivated by heat and humidity over time. 65°c for 20 minutes @ 50% RH will do it for most. Adenoviruses are a bit hardier and generally require about 70°c for 20+ minutes.  In most cases, particularly in a well ventilated sauna, there is little risk of transmission of airborne pathogens such as cold or flu. That I know of I have never gotten a cold or flu from someone I’ve sauna’d with and it is not a concern. That said, nobody with Covid (a highly transmissible virus) should use a public sauna and I would not share a sauna with someone who has Covid. While successful transmission is less likely in a properly ventilated sauna the outcome, long-covid or death, carries a far greater risk.

Foot bacteria and fungi that get deposited on the foot bench are similarly killed by heat and humidity of saunas in Europe. This is not the case of saunas with low benches such as is common in the U.S. where temperatures and humidity rarely or never achieve the temps required so here a greater concern.

 

What’s A Sauna?

If we want any health benefits attributed to sauna then we need to know what a sauna is and what’s critical from a health/medical standpoint. If a specific benefit requires that we raise our core temp by 1°c in each of 3 sessions but we raise it by only 0.4°c per session because of higher temp stratification then we’ll not have achieved the benefits we’re after.

So what’s likely critical?

Ventilation – Most studies have been conducted in saunas that likely have much better air quality than a typical North American sauna with poor ventilation. The higher CO2 and VOC levels in North American saunas may actually be doing more harm than good. This particularly in public saunas such as in gyms and fitness centers where pathogens and other gook may fill the air.

There are two elements to this:

  • Removing CO2 from our body is critical to all metabolic functions. Too high of CO2 in a sauna can result in too high of blood CO2 which can impede muscle recovery.
  • Besides the direct problems of too high of CO2 levels, there’s an important indirect element – time. Higher CO2 levels cause us to leave a sauna sooner. In one example, three of us who sauna quite regularly and typically spend about 15 minutes in a 90°c sauna, could only stay in an 80°c sauna for an average of ≈11 minutes (averaged over 4 rounds). That’s less time we’re exposed to heat and so less increase in core temp or localized exposure to heat.

CO2 levels should ideally be below 550 ppm though as high as 700 or maybe even 1000 is OK.  

An Aranet4 placed where temps never exceed 50°c should provide a good indication of ventilation. Keep in mind that in some or most saunas the actual levels are likely 10-20% higher than what the Aranet4 will read.

More on the effects of CO2 in saunas: How Carbon Dioxide Affects Sauna Air Quality.

Even Convective Heat – For most health benefits you’re trying to affect your entire body, your core temperature, not just your head and shoulders. Probably 99% of saunas in North America have too much stratification and so even at 220°f (temp near the ceiling) your body is still not getting the health benefits that it would in a 170°f sauna in Finland that results in an overall higher average temp (and is much more comfortable and enjoyable). Doctors at Thermé Wien Medical Center in Austria told me that if bathers feet are more than about 18-22% cooler than the bathers head then they are likely not getting proper health benefits.

Core temp is effected by the amount of heat each region of our body is exposed to for what time period.

Regional percent body surface area BSA in the adult Adapted from Lund and Browder 35 3

Here we can see that our feet make up 7% of our skin surface, our lower legs make up 14% and our upper legs 19% for a total of 40% of our skin surface. If our entire body is evenly exposed to 90°c heat then we can say that’s 100% effective. If on the other hand our feet are only 60°c, our lower legs 64°c and our upper legs 67°c then we’re not getting the same benefit.

Knowing how the temperatures stratify in a sauna and so approximately what temp each region of our body is exposed to allows us to get a rough idea of effectiveness of different experiences.

  • Good Sauna (18% head to toe difference): 84% effective
  • Acceptable Sauna (22%): 81%
  • Barrel (50%): 56%

So a barrel for example is about 1/3 less effective than a good sauna for any given amount of time. 

Note that this does not take in to account different sensitivities of different regions nor any potential effect from breathing in hotter air nor that heat effect is not linear.

Similar to CO2, greater head to toe temps can be less comfortable so we stay in the sauna a shorter period of time. 

Taken together, a barrel might provide only about 25-50%% as much benefit as a sauna with less stratification and CO2. A big question here then is if that is enough?

Radiant vs Convective – Some studies confuse radiant and convective heat and call both ’sauna’. The heat from a convective heat sauna will in many cases likely produce different results than the radiant heat from an IR booth, Laconium or Sweat Cabin. We do not yet have a good idea which produces what benefits nor which is potentially better. Also, Waon therapy (IR) is popular in Asia while doctors in Europe seem to believe ultrasonic is better than IR (and all of these different from the benefits of sauna).

Healthy Lifestyle.– Many of these studies have been on a population such as Finland that is much healthier due to a healthier lifestyle than a typical North American and this will likely affect outcomes.

Definitions. There is a definitional problem. A study may say that a ‘sauna’ has benefits A, B and C. But what’s a ‘sauna’?  In Finland and some other countries it would be well understood to be what’s discussed throughout Trumpkin with the characteristics listed at the beginning of Trumpkin’s Notes on Building a Sauna. Probably less than 1% of saunas in the U.S. meet those criteria though so we don’t know what health benefits would accrue from use of these. Studies by Dr. Jari A. Laukkanen, Earric M Lee and others that show proven benefits have likely not included frequent extreme cold plunges for instance but rather much more moderate hot/cold contrast. In at least one study ‘sauna’ was used to describe an IR Cabin. 

There is a need within the spa and sauna industry to clearly define what various experiences are and in the medical research community to do a better job of describing exactly what protocols were followed with what experiences.

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Gym Saunas and Barrels – EVERY gym sauna that I’ve been to in North America (and the UK) has had noticeably poor air quality and quite high stratification. These are not only not as enjoyable as a real sauna but likely offer no health benefits and may do more harm than good. Personally I’d stay out of them. Similarly, the barrels sold in North America.

If you want any health benefits then you want a proper sauna with good ventilation and higher benches for low stratification.

 

 

Health – Myths

There are a lot of myths about sauna in the U.S. compliments of deceptive marketing by sauna companies. This is particularly a problem with IR booths (which are not actually sauna). The two big ones are weight loss and sweating out toxins:

1) Sauna does not cause weight loss. You’ll loose some water weight and maybe a calorie or two from a higher heart rate but that’s about it. And you should also drink enough water (or beer or longdrink) to make up for that. 

Some people report that their sport watch says that they burned xxx calories in the sauna. The problem is that the sport watch is measuring heart rate and it’s assuming that the higher heart rate is caused by physical muscular activity which would indeed cause calorie burn. But in this case our higher heart rate is caused by heat, NOT by physical muscular activity. If Apple and Garmin had an activity called ‘Sauna’ then it would indicate little beyond normal metabolic burn.

In a podcast recently Dr Peter Attai noted that in measuring lactate levels while in the sauna that he did not even reach zone 2 (which is an extremely low caloric burn), much less anything higher where measurable calorie burn takes place.

2) As far as I know there is no real thing as sweating out toxins – not in a sauna nor steam room nor IR booth nor anything. Sweat is water and salt. And a very tiny bit of minerals. That’s it. Your liver and kidneys deal w/ mineral based toxins, they are simply ancillary in sweat and the amounts no more than a rounding error.

Sweating in a sauna can sweat out gook in your skin though. Bacteria and soap scum the primary elements for most people but also potentially the embedded particulate matter from things like spray painting or firefighting. It’s critical to have proper ventilation.

If you use mineral based sunblock which can be very tough to wash off, a round or two in the sauna AFTER a good soap shower will get some or most of what soap doesn’t. 

 

Health – Benefits

First, sauna should be totally enjoyable. It should not be uncomfortable drudgery done purely for health benefits. If it’s not enjoyable then it is likely because the sauna does not have proper ventilation or proper heat so if you’re not enjoying it then find a real sauna. That said, there is a bit of acclimation necessary both for those new to sauna and to some extent with each sauna session. In a well-built sauna with proper ventilation and heat the first round is often a bit of a acclimation round and not quite as enjoyable as subsequent rounds that often get better and better with each round.

Finns frequently say that they never sauna for any reason. They don’t sauna for health benefits but only for enjoyment. The health benefits are just a side bonus. And that’s all very true. HOWEVER, I personally think it’s totally fine to go to sauna for the health benefits. Importantly, enjoyment is one of the key health benefits. If it’s not totally enjoyable then you likely need a better sauna with proper bench and ceiling heights, ample volume per bather, air gaps in and behind the benches, and other bits that make a good sauna a good sauna.

Perspective – In the overall scheme of things the health benefits of sauna are not particularly great and will likely not make up for lacking in other areas. Staying physically & mentally active and eating well are of far greater importance. Riding a bicycle for local transportation will provide perhaps 15-20x the benefit of sauna. So while there are indeed likely health benefits to sauna, keep their contribution to your wellbeing in perspective. As well, most of the studies have been on populations in Finland who lead a much healthier lifestyle than Americans. They live five years longer but more importantly have many fewer disability years so they may benefit more from sauna than a typical sedentary American. 

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Perhaps the first and most key health benefit is that sauna, done properly, is relaxing, improves our mood and mental state and may reduce anxiety. Medical folks attribute this to the practice itself, our bodies response to hot cold contrast and exposure to negative ions.

Likely as important is the social element of sauna. Sweating in common with others in such a peaceful and relaxed atmosphere.

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There are a number of studied and proven health benefits to sauna. Some of these benefits are believed to come from the cycling of hot/cold/hot/cold/hot/cold – contrast therapy. Others from sweating, and others from relaxing heat. Potential health benefits include:

  • Improved cardiovascular system, significantly lowered risk of Congestive Heart Failure, and lower risk of blood pressure disorders, coronary heart disease, stroke and heart-related sudden death.
  • Lowered risk of Ischemic Heart Disease / Coronary Artery Disease, Peripheral Artery Disease, Dyslipidemia, and Hypertension
  • Reduced risk of Dementia, Alzheimers, Depression, Cognitive Decline and related issues.
  • Reduce some negative elements of Rheumatism / Rheumatoid Arthritis.
  • Better Sleep. Many people report that a sauna session in the evening or before bed can help them relax and sleep better.
  • Decreased stress.
  • Stronger immune system.
  • Decreased inflammation. 
  • Maybe improved skin.
  • After a workout sauna can help muscles relax and begin the repair process.
  • There is some evidence that regular sauna may lengthen telomeres.
  • Tinnitus relief. I’ve had a ringing in my ears since an incident about 10 years ago and it was made considerably worse by a noise at the end of 2020. Both ENT’s that I saw about it recommended regular massages as the only known relief but both agreed that it wouldn’t hurt to try sauna. While regular sauna may not work as well as massage it does work noticeably well (and is a bit less expensive) especially when done about every other day. 
  • Negative Ions. There is some evidence that negative ions, such as those in a traditional sauna from pouring water on the stones, may be beneficial. How beneficial still needs some research. Note that water on steel or iron (e.g., stoves) produces positive ions and should be avoided.
  • Social. There are significant mental and thus physical benefits to simply doing something enjoyable with others and this may be the greatest benefit of all.

“Research by Dr Jari A. Laukkanen M.D., an internal medicine and cardiovascular diseases specialist, also observed that heart and cardiovascular disease mortality decreased as the number of minutes spent in the sauna increased: There were half as many deaths among those who spent more than 45 minutes a week in the sauna than among those who spent less than 15 minutes in the sauna.”  

“Men who took four to seven saunas a week had a 66 percent smaller risk of a dementia diagnosis than those who sweated it out once a week.”

Thermé Wien Medical in Austria is a world leading clinic for Rheumatoid Arthritis and related conditions. They have had some good results with contrast therapy utilizing sauna + cold plunge. This is something that goes back at least 150 years as when Dr. Barter built his first Victorian Roman Bath facility in Ireland it was for treatment of Rheumatoid Arthritis and showed good results then. This is just the first documented bit and positive results likely go back hundreds of years prior.

Some good discussions on the health benefits: Mayo Clinic: Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence , Dementia and Alzheimers Study, Health Secrets Of The Sauna, , and Found My Fitness.

A recent episode of The Upper Bench podcast is very much worth watching: The intersection of sauna health, science, and culture with Dr. Mark Timmerman.

 

A Word Of Caution – As time goes on we learn more and more about the world around us and our own physiology and neurobiology. We learn about what is good, not so good and downright bad. What we’ve learned about Oxytocin over just the past 5 to 10 years, for example, borders on astounding. Over the past 5 years we’ve learned that what we thought we knew for decades about lactic acid likely isn’t really so. And then of course we’ve learned a lot about CO2 and Indoor Air Quality over the past 5-20 years.

We are learning a lot currently about contrast therapy, both hot+cold bath and sauna+cold bath as well as cold therapy alone. I’m a fan of these. There’s good science to back up much of what we’re learning. But we’ve still much more to learn than we already know. 

Some people, particularly some bloggers and podcasters, get out ahead of the science and too often without any caveats. They may say what will get them PR and paying members rather than what is accurate. Be careful what you believe.

One more interesting bit. Thermé Wien Medical and others are finding that for anything where IR might be a good or better option to Sauna, Ultra-sonic appears better than IR including for treatment of rheumatoid arthritis and ankylosing spondylitis. My understanding is that they are no longer using any IR/Radiant thermal treatment and are focusing on sauna (convective heat), hot water bath, wraps and ultrasonic only.

* Some or many of the health benefits may not be realized in American saunas with poor quality heat and poor ventilation. Similarly, poor ventilation and large head to toe temperature differences, both common in American saunas, may have negative health consequences.

 

Health Perspective – Blue Zones

The healthiest people in the world do not, as far as I know, ever go to sauna nor do any kind of thermal therapy – hot, cold, contrast or anything. They stay active with things like bicycling for their local transportation, eating wisely, staying close to family and other bits that result in an overall healthy lifestyle.

BZ9

So, while there may be some health benefits to sauna, there are other things vastly more important to a healthy life. If you’ve not already I highly recommend reading Dan Buettner’s ‘The Blue Zones: Lessons For Living Longer’.

 

Post Workout Sauna

While a sauna round or three after a workout may feel great, it may not be beneficial, especially in typical U.S. gym saunas. Things to consider:

  1. Hot vs cold vs contrast.
  2. Saunas in U.S. gyms often have poor or even no ventilation resulting in high CO2, airborne bacteria and other contaminants. 
  3. People bringing bacteria in to the sauna:
    1. Not showering with soap before entering.
    2. Wearing clothes in the sauna (see: Sauna’s, Nudity & Victoria)
  4. Some U.S. gym saunas have treated the wood with chemicals (sealers) that are quite harmful to breath.
  5. U.S. gym saunas rarely (e.g., never) have sufficiently high benches, so bathers experience considerable stratification.
  6. Gym saunas in the U.S. are often not located where it is easy to go outside for fresh air and cooling off.

Many, and perhaps all, of the benefits of post workout sauna are likely from the hot/cold contrast, not from just the sauna heat itself. Sauna alone may actually do more harm than good as it will cause inflammation and non-beneficial stress while repeating hot/cold contrast appears to improve ventilation (intake of O2 and exhaust of CO2) and blood flow that leads to faster and better recovery and healing.

However, just as with contrast hydrotherapy, we don’t yet have very good data beyond anecdotal. There is also some evidence that post workout contrast therapy may aid recovery but reduce building of muscle so if gaining muscle size rather than strength or general health is your goal then sauna or contrast therapy may not be the thing.

Many athletes report faster recovery and less likelihood of severe DOMS when workouts are followed by a 3 round sauna session. Some studies may indicate that cold hydrotherapy or cryotherapy may work almost as well (having done both, I’ll take the sauna version of contrast therapy!). The contrast therapy from multiple hot/cold sauna rounds appear to reduce lactic acid that’s built up during a workout or sporting event. So does cryotherapy, though sauna MAY be more effective. 

Proper ventilation is critical. Too much CO2 (above about 550-700 ppm) in the sauna hot room will result in too high of blood CO2 which will hamper your body’s ability to recover. For this reason, going to a typical U.S. sauna with poor ventilation likely does more harm than good. Some good information on this is now publicly available here and in particular the article ‘Elevated CO2 Levels Delay Skeletal Muscle Repair by Increasing Fatty Acid Oxidation’. BTW, this applies to your gym, locker room and elsewhere as well. You can do a harder workout and get more benefit if CO2 levels are kept below about 700 ppm.

Stratification and Cold Feet. To get benefit from sauna you need to be heated evenly over your entire body. Most U.S. gym saunas have too low of benches so there is often a 40°c or greater head to toe difference (you want no more than about a 22% head to toe difference). Your head is hot, your abdomen is warm (relative to your head) and your legs are cool (again, relative to your head). This can actually hurt recovery rather than help.

Bacteria. Not showering well and/or wearing clothes in a sauna results in increased bacteria for everyone. It’s critical that ALL sauna bathers shower well before entering and either be nude or wear as little cloth as possible. Skin covered in cloth doesn’t breath well and becomes a haven for bacterial growth …and the odors that come with it.

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Where I’ve personally found it most beneficial is after weight days. My routine is Mon/Wed/Fri are weights and Tue/Thu/Sat are cardio (usually rowing, bicycle or nordic skiing). Post weight day workout I’ll typically do 3 rounds though it sometimes varies from one to five. Each round is 10-15 minutes in the sauna (usually about 203°f) followed by cooldown (jump in lake summer or winter, or cold shower and then outside for a bit in winter if there’s no hole in the ice). I usually lay down for the first half of the first round and then sit but that’s purely personal preference.

I do think that I notice a difference when I do and do not go to sauna afterwards. Whether there is actually a difference or just a difference in my head I don’t know.

If you like a post workout protein shake it may be a good idea to start it a bit earlier and drink it slowly over 15-20 minutes so that by the time you begin your sauna rounds it’s not all just sitting in your stomach which can be less than fun when you hit the first cold part.

Dr. Rhonda Patrick and Joe Rogan are known for promoting sauna use with workouts which is good. They have both also shown a lack of understanding of sauna (surprising for Patrick) and of how the health benefits work. Or perhaps they both just say what they believe will sell and get them listeners and paying members rather than honest info. FWIW, most Finns I know do not regard either of them very highly for their sauna knowledge. I would take anything they say with a giant grain of salt.

 

Post Work Sauna

Sauna after a long days work has the benefits of helping us to relax mentally and physically, likely helps with muscle recovery and is enjoyable.

There’s one other benefit though – cleanliness. There’s no such thing as sweating out toxins, but we can sweat out some of the gook in or on our skin. Along with this, and similar to aiding muscle recovery, we may begin tomorrow with cleaner pores which may allow us to sweat easier and thus remain cooler on a hot day.

 

 

Is EMF A Concern?

Not likely in a sauna but possibly in an IR booth.

Every heat source (and really everything) in the world emits EMF, including every light bulb and every surface in your home. And each of us. And sauna heaters. Here’s an image of the EMF spectrum.

EMF

Whether the EMF emitted from a sauna heater is harmful or not we kind of really don’t know as we’re still learning about physiology and how our bodies and the world around us interact.

What we do know is that well done studies (above) have indicated that people who sauna (room heated by stones) frequently tend to have fewer health problems (particularly heart ailments and dementia), live longer and show no obvious adverse effects compared to those who sauna less frequently or not at all. So if EMF is causing some harm then the benefits of sauna appear to outweigh any harm.

FWIW, I’m far more concerned about particulate matter (PM1.0, PM2.5, etc.) in a sauna than EMF.

IR Booths might be a greater EMF concern for a number of reasons but we don’t really know for sure. Unfortunately we also don’t have the health studies as we do for sauna. Any harm likely comes from dosage being built up slowly over time and it will vary by unit and the individuals using it. Not unlike getting skin cancer from being in the sun or a tanning bed – except slower. It could be that for a particular IR Booth and individual a total of 20 hrs of total lifetime exposure does little or no harm, 60 hrs total does minimal and 200 hrs does considerable harm. A different unit might be 2x or 3x those dosages. Or none cause any significant harm with less than 500 hrs. We don’t know.

Don’t believe anyone who states that there is no risk or minimal risk because again, we don’t know and will not know until some long-term studies can provide solid data one way or the other.