Sauna Science Addendum 2: Wet or Dry?
Is the steam room (i.e. wet sauna) as useful as a typical dry sauna?
If you read Shortcut U’s deep dive, Sauna Science, you’re aware of some of the research suggesting that, rather than just a hot bench to gossip on, the sauna is a significantly useful tool for health and fitness.
Interestingly, in addition to the dry sauna–what I figure most people envision when they think of the sauna–some of the research I covered in that deep dive suggested there are benefits to other flavors of heat therapy, such as one study that showed decreased vastus lateralis (one of the quadriceps muscles) atrophy when using localized heat therapy on the thigh. (I)
On this topic, one question I’ve come across repeatedly is whether the wet sauna, also known as the steam room, likely offers similar benefits to the dry version. If you asked me this even a year ago, I likely would have bet that the answer was no, leaning on the concept that the steam room doesn’t get as hot as the dry sauna because the water would burn you if it did.
However, after recently starting to use the steam room regularly, I decided to take a look into some research on this modality of heat therapy as well as how it compares to the standard sauna. And, I’m fairly convinced I was way wrong with my previous conclusions.
If you’re interested in reading research about sauna-use, Patrick and Johnson’s review is the best resource I’ve read yet for essentially all things sauna. (V)
How Does the Steam Room Work?
Before we get into some data, let’s cover what I got wrong about the basics of the steam room.
As I described above, I didn’t think the steam room would be as effective as the dry sauna because water will burn you at a lower temperature than air due to water being a better conductor of heat. For this reason, I figured that the temperature of a steam room would not be as high as in a dry sauna, and I was correct about this part.
What I got wrong is that this would mean a wet sauna wouldn’t be able to get your body as hot. Though the temperature of the steam room is lower than in a dry sauna, the increased humidity in a wet sauna interferes with the body’s ability to cool down because it makes it more difficult for sweat to evaporate off of your skin–the main mechanism through which sweating facilitates thermoregulation. (IV)
“High air humidity in a wet steam bath causes difficulties in evaporation of sweat from the surface of the skin. This may slow down the removal of heat from the body.” (IV)
So, although the wet sauna does not get as hot as the dry sauna, it can hypothetically increase body temperature similarly by impeding the body’s ability to shed heat in what are still fairly hot conditions. But, does data back this hypothesis up?
Wet vs. Dry Sauna
I only found three studies comparing the wet sauna and dry sauna; however, all of them tended to show that the wet sauna elicited similar or greater physiological effects as compared to the dry sauna regarding heart rate, body temperature, and/or blood pressure. (II, III, IV)
This comes with the major caveat that I could not get access to the full texts of two of these studies (one because it was only available in Polish), meaning that I am purely going off of what is written in their abstracts–something I typically avoid and find to be highly problematic.
With that said, those two abstracts (II, III) clearly described similar or greater effects of wet sauna on heart rate and rectal temperature compared to the dry sauna intervention. Also, one of these studies (II) has the same first author as the study discussed below that I did get full access to (IV), and these two studies seem to have a similar design only with one in females and the other in males.
“Ten women aged 22-24 years took part in the study. A session in each sauna lasted 60 min and consisted of 3 thermal 15-min exposures, in 5-min intervals for rest and cooling with water. The temperature in the dry sauna was 91±1.2°C and in the wet sauna 59±1.3°C, while the humidity was 18±0.7% and 60.5±0.8%, respectively…The average weight loss after a dry sauna bath was significantly higher than after a wet sauna bath. Significantly higher increases in Tre [(rectal temperature)], as well as in HR [(heart rate)] were observed after treatment in the wet sauna, compared to the dry sauna. Both treatments resulted in an increase in SBP [(systolic blood pressure)] and a decrease in DBP [(diastolic blood pressure)].” (II)
“Sixty subjects, 33 males and 27 females, from 18 to 63 years of age, were exposed to two kinds of saunas: the Finnish sauna (dry sauna) with an air temperature of 80 to 90 C and a relative humidity of 50%, and the wet sauna with an air temperature of 45 to 50 C and a relative humidity of 100%. There was a rest period of one week between the two experiments. For the 60 subjects the mean duration in the wet sauna was 19.6 minutes and in the dry sauna it was 17.4 minutes…Comparing the different physiological parameters in both saunas showed significant differences only during the first 10 minutes: a greater drop in diastolic blood pressure, a higher increase in systolic blood pressure, and a greater rise in pulse rate in the dry sauna. After 20 minutes there were no significant differences between any of the above parameters. It is concluded that the heat strain and hence the risk in both saunas are similar and exposure in either sauna exceeding 10 minutes may be dangerous.” (III)
Notably, Schoenfeld and Colleagues’ paper (III) is from 1976, so their conclusion that, “exposure in either sauna exceeding 10 minutes may be dangerous,” is likely outdated, in that it is more cautious than current scientific views on the sauna that I am aware of. As Patrick and Johnson describe in their review paper from 2021, “sauna bathing is associated with many health benefits, from cardiovascular and cognitive health to physical fitness and muscle maintenance. It is generally considered safe for healthy adults and may be safe for special populations with appropriate medical supervision” . (V)
The one study for which I was able to access the full text for showed similar results when comparing their wet and dry sauna protocols, which consisted of three rounds of 15 minutes of heat exposure separated by 5-minute rest periods that included 2 minutes of exposure to cool water. (IV) Notably, the wet sauna and dry sauna experiments were separated by one month and entailed ~138 degrees fahrenheit at 60.5% humidity and ~196 degrees fahrenheit at 5-18% humidity, respectively. (IV)
“Subjects underwent a cycle of dry sauna bath (Exp I) and wet steam bath (Exp II) divided by a one-month break. Each bath lasted 60 minutes – 3 x 15 minutes in a sitting position in a hot chamber with 5-minute breaks between exposures. During breaks subjects cooled their bodies for 2 minutes with water of 22°C and after that they rested in a sitting position. The average temperature in the dry sauna was about 91°C with humidity of 5-18%, and 59°C in the wet sauna and 60.5% humidity.” (IV)
The researchers measured the subjects’ heart rates manually at their carotid arteries every 5 minutes throughout each protocol and tracked the subjects’ body temperatures continuously using a rectal thermometer. (IV) They found that both protocols significantly increased subjects’ heart rates and rectal temperatures on average and that the wet sauna increased these metrics statistically significantly more than the dry sauna. (IV) Specifically, the respective average heart rates and rectal temperatures were 126.0 vs.138.2 beats per minute and 38.05 vs. 38.50 °C following the last round of the wet and dry sauna protocols, respectively. (IV) (See Figure 1 From the study below for a visual)
Interestingly, the researchers also tracked the subjects’ personal senses of heat stress using a survey called the 7-point Bedford Scale that ranges from, “much too cool,” to, “much too warm.” (IV) The results for this subjective metric were similar to those for heart rate and rectal temperature, showing significant increases in both groups and statistically significantly greater increases in the wet sauna compared to the dry sauna during the second and third rounds. (IV) (See Figure 2 From the study below for a visual)
Additionally, the dry sauna protocol led to about twice as much weight-loss as the wet sauna protocol (~1.6 lbs vs. ~0.80 lbs, respectively), which makes sense to me considering the hypothetical increase in sweat loss while in the dry sauna. (IV) And, at the close of the three rounds, both protocols led to average increases in systolic blood pressure (+20.0 mmHg vs +17.7 mmHg for dry vs. wet sauna, respectively) and decreases in diastolic blood pressure (-15 mmHg vs. -20 mmHg, for dry vs. wet sauna, respectively), the former of which was statistically significantly greater following the dry sauna protocol and the latter of which was statistically significantly greater following the wet sauna protocol. (IV)
Conclusion
Where does this leave us?
The data I found is limited–especially considering I am only going off of abstracts for two of the three studies I cited–but it is consistent, in that it all suggests that the wet sauna elicits similar physiological effects as the dry sauna, at least. And, based on my previous deep dives into research on sauna-use, as well as what I’ve heard listening to experts, like Rhonda Patrick, it seems that these physiological responses—mainly increased heart rate and increased body temperature as far as what we’ve discussed in this post—are a significant part of what drives the health benefits of sauna-use.
Further, my personal experience using the steam room reflects what Pilch and Colleagues found regarding subjects’ subjective feelings of heat stress (IV) , in that I feel just as hot in the steam room as I do in the dry sauna, if not hotter. And, when checking my pulse manually in the steam room, I find that my heart rate increases comparably to that when I am in the dry sauna–notably, I consider myself fairly adapted to the dry sauna, in that I typically go in for ~15 minutes at 195 degrees fahrenheit or hotter.
As far as what I’ve found, the wet sauna is considerably behind the dry sauna in terms of data—especially longer-term data; however, considering the mechanism of reducing sweat evaporation, limited but consistent data, and my personal experience all together, I have switched to being more bullish on the steam room.
In particular, I have been using the steam room lately because the dry sauna at my current gym does not get hot enough for me–I’m barely sweating and have only a slight increase in heart rate after 20 minutes–while the steam room provides a heat stress seemingly similar to those of sufficiently hot dry saunas I’ve experienced.
What are your thoughts? Have you tried the steam room, and how do you think it compares to the dry sauna?
If you liked this post, I bet you’ll like my previous posts about sauna: