Saunas are a form of heat therapy created in Finland that involves going into a heated room, typically for 10-30 minutes at a time, and sweating a lot. They are a fixture in Finnish culture, and like many cultural practices, sauna bathing has been proposed to have various health benefits. These benefits include improved cardiovascular health, improved mood, decreased stress, and decreased pain, as well as many others.
Unfortunately, the claims surrounding sauna use are always not constrained by strong scientific studies. In this article, we will go through the proposed health benefits, scientific investigations, and safety risks of sauna use.
A typical sauna is a small, wood-panelled room with a radiant heater, although the heating source can vary depending on construction. It is typically kept at 70-100° C or 158-212° F, and 10% to 20% humidity. Humidity is maintained by pouring water onto the hot surface of rocks inside the sauna. Total treatment times vary, but they typically involve two to three rounds of exposure of up to twenty minutes, followed by cold immersion in normal temperatures.
Another type of sauna, called infrared sauna, utilizes incandescent lamps to generate heat. Infrared saunas do not get as hot as the traditional Finnish-style sauna, only reaching 45-60° C, or 113-140° F, and there is no focus on humidity control (2).
What Is The State Of The Research?
Many researchers have looked into the proposed health benefits and potential risks of regular sauna use, and as a result, there are a fair number of articles available on various topics. A group of researchers from Finland have investigated the benefits of traditional Finnish sauna. In addition, a group of researchers from Japan have investigated their own infrared sauna therapy, termed Waon Therapy. The majority of the research I came across focused on the relationships between sauna use and cardiovascular, musculoskeletal, and psychological conditions.
Despite a long history of sauna use, the research performed thus far is only preliminary. There are very few randomized controlled trials with a large amount of participants. Many articles are only case reports describing a few people.
The larger-scale studies only looked at associations between sauna use and various health outcomes, which are typically not used to determine if the treatment in question is actually effective. In addition, there were no studies I came across that compared sauna use to similar interventions designed to produce the same outcomes, like exercise, weight loss, or other forms of heat therapy. What exactly does the current research say?
Do Saunas Help Relieve Pain?
A randomized controlled trial was performed looking at the effects of sauna use versus advice and education on 31 patients with chronic tension headaches. The researchers found that after eight weeks, the sauna group had slightly less intense headaches as compared to the control group. However, there were no differences between both groups for headache duration, sleep changes, depression, or on the Headache Disability Index (3).
A study of 46 patients with chronic pain looked at the effects of cognitive behavioral therapy (CBT), rehabilitation, and exercise therapy, and half of the participants also got Waon Therapy. They found that after six weeks, both groups had significant improvements in pain, pain-related behaviors, and measures of mood. However, the Waon Therapy group improved slightly more, and outcomes were better two years later (10).
Despite some positive results, there was no control group that received no treatment to evaluate the natural history of chronic pain, and the way they measured some of the outcomes were not valid or objective.
Two studies from the same researchers looked at the effects of thermal therapy on 12 total patients with chronic fatigue syndrome (CFS). Both groups of patients saw some improvements in pain or perceived fatigue (11, 17). However, studies with a small number of patients and no comparison groups, while interesting, aren’t strong enough for us to say anything definitive about sauna use.
Another study from Japan looked at the effects of Waon Therapy for patients with Fibromyalgia, a disease associated with widespread pain, among other symptoms. 13 participants underwent ten sessions of Waon therapy and by the end of the treatment, all patients had a reduction in their pain levels by about three points out of ten (13). But again, like the previously mentioned study, having such few patients and no control group does not allow us to make strong conclusions about effectiveness.
In a larger-scale Japanese study, 44 patients with Fibromyalgia underwent Waon therapy as well as underwater exercise for 12 weeks. The researchers found average pain scores were decreased by the end of the study by about four points out of ten, with an effect maintained after 6 months (12). While this study did have more participants, there were no comparison groups, limiting our ability to see if Waon Therapy is actually effective.
Rheumatoid Arthritis and Ankylosing Spondylitis
36 patients with either rheumatoid arthritis (a disease characterized by widespread pain in the joints caused by an autoimmune response) or ankylosing spondylitis (a disease characterized by inflammation and stiffness in the back) underwent infrared sauna treatments for four weeks. All subjects had small reductions in pain after the first session, but after all sessions were completed, there was essentially no net change in pain levels on average (14).
Small, low-quality studies without appropriate placebo or comparison groups show sauna therapy is associated with a small reduction in pain, but there is no evidence from strong studies that sauna therapy can actually relieve pain, or that sauna therapy is better than any other therapy.
Do Saunas Help Release Toxins?
Many claim that sweating can help reduce the build-up of toxins in the body. There are no studies at all that looked at sauna use and the “toxin” content of a person’s sweat. As pointed out by Dr. Dee Anna Glaser in an LA Times article from 2008, although sweat does contain trace amounts of toxins, its main purpose is to cool you off. The kidneys and liver help to detoxify you and there is no need to spend time in a sauna to rid your body of toxins (19).
While it sounds superficially plausible, there is no evidence that saunas can help release toxins in your body. Any suggestion otherwise is merely speculation or a marketing claim not backed by science.
Do Saunas Help Improve Cardiovascular Health?
Deaths Due To Heart-Related Conditions
One study from Finland looked at the correlation between sauna use and death due to heart-related conditions for 2,315 men. The researchers started the study in the mid-1980s by quantifying weekly sauna use of each subject. The researchers also assessed body mass index, smoking and alcohol history, physical activity levels, various blood measurements, and the presence or absence of clinical conditions like diabetes, coronary artery disease, stroke, and others.
They found increased sauna use was associated with a decreased risk of dying from sudden cardiac events, coronary heart disease, and cardiovascular disease (8).
There are a few problems with this study that the researchers discuss. They only performed assessments of sauna use and other factors when they first started, opening the possibility for those variables to change over time. We don’t know if each subject maintained their reported weekly sauna use, despite it being common cultural practice.
In addition, there could be another variable that plays a role, like a healthy diet. Lastly, it is important to emphasize what type of study this is. A correlational only allows us to see if there is an association between two events and does not allow us to conclude a cause and effect relationship.
Multiple studies have looked at the acute effects of sauna use on blood pressure. One study looked at the effects of a single sauna session on 109 patients without any symptoms of cardiovascular disease. They found that average systolic blood pressure decreased from 137 to 130 immediately after the sauna, and remained at 130 when measured 30 minutes after. Diastolic blood pressure went from 82 to 75 immediately after, and back up to 81 when measured 30 minutes after (7).
The same group of researchers also looked at the associations between sauna use and the development of high blood pressure for 1,621 Finnish men. They found that men who reported they utilized the sauna more frequently at baseline were less likely to go on to develop high blood pressure over a period of 22 years. However, the researchers did not track sauna use over time and only relied on what the participants indicated they did at the beginning of the study (20).
The same core group of researchers from Japan have performed a number of studies on the effects of sauna use on patients with heart failure. A study on 129 patients with chronic heart failure revealed that undergoing Waon Therapy resulted in less cardiac-related deaths over a five year period as compared to controls who didn’t receive the heat treatment (4).
Another study on 49 patients with chronic heart failure revealed that undergoing Waon Therapy resulted in improved ejection fraction (a measure of how much blood the heart can output), and slightly improved performance on a six-minute walk test (16). Lastly, a study of 149 patients with chronic heart failure found that when compared to the control group, those in the Waon Therapy group had slightly decreased levels of B-type natriuretic peptide (an indication of the severity of heart disease), as well as improvements in the six-minute walk test, among other things (18).
There is weak, preliminary evidence that sauna use is associated with small improvements in blood pressure and other measures of cardiovascular health. Many of the studies were very small, had no control groups, or did not compare sauna use to other treatments like other heat therapy, exercise, or changes in diet. The results of these studies are interesting, but do not yet show definitive benefits.
Do Saunas Help Decrease Stress?
I was unable to find any studies that specifically looked at sauna use and stress. Some of the previously mentioned studies reported that participants has small improvements on measures of quality of life.
There are no studies available that show sauna use can help reduce stress, but like any other activity that is perceived to be relaxing or allows for some mindfulness, it may be beneficial.
Do Saunas Help Skin Problems?
I was unable to find any studies that specifically looked at sauna use and any skin problems.
There are no studies available that show sauna use can help people with skin problems and any suggestion that it can is merely speculation or a marketing claim.
Do Saunas Help With Respiratory Diseases?
A correlational study of 1,935 Finnish men over 25 years looked at reported sauna use. The study found that increased sauna use was associated with a lower risk of developing COPD, asthma, or pneumonia (6). A small study of 20 people with chronic obstructive pulmonary disease showed a course of Waon Therapy improved measures of air inhalation and expiration, but had no changes on an exercise capacity test, as compared to controls (5).
Two studies hint at a potential relationship between sauna use and respiratory disorders, but this needs to be further explored.
Do Saunas Help With Immunity?
One study from 2013 investigated the effects of a 15-minute sauna session on 18 participants. Researchers found that in both study groups (athletes and non-athletes), a few types of white blood cells (WBC), which help fight disease, were increased (15).
The results of this study have been drastically misinterpreted and exaggerated by those in popular media, and many have suggested that this shows sauna use may improve your immune system and prevent disease. This is simply not the case, as this study only had 15 people go in a sauna once, and measured their WBC count before and after. The researchers did not look at how long this effect lasts, if it is actually correlated with getting sick less often, or how it compares to other treatments.
There is weak preliminary evidence from one very small study that shows sauna use changes white blood cell count, but there is no evidence that this effect lasts or correlates sauna use with being sick less frequently.
Do They Lower The Risk of Dementia And Alzheimer’s?
The same researchers from Finland looked at the association between sauna use and dementia and Alzheimer’s in the same group of 2,315 participants. After baseline assessments, they tracked each participant over time, and noted how many people developed dementia and Alzheimer’s disease. They found that after they accounted for the other variables that could have played a role, increased sauna use was associated with less risk of developing dementia and Alzheimer’s (9). Unfortunately, this study suffers from the same problems as mentioned above.
There is one large-scale correlation study that shows preliminary evidence that using the sauna is associated with a decreased risk of developing dementia and Alzheimer’s but there is no experimental evidence that shows or hints at this relationship.
Are Saunas Safe?
The majority of studies I read either reported no adverse events from sauna use or did not mention safety at all. According to one author, “for most healthy people, as well as for most patients with stable coronary heart disease, sauna bathing is well-tolerated and safe” (1). However, one author found that there are some reports of burns, ischemia, syncope, and even death (2).
Due to these risks, common sense safety recommendations apply: remain well hydrated, avoid anything that can affect hydration status like alcohol, limit sauna exposure to 10-30 minutes, and exit the sauna if you don’t feel well. If you have questions or doubts about your ability to go in a sauna or an extensive history of cardiovascular disease, ask your doctor prior to doing so.
What Can We Say With Certainty?
- The research on sauna use thus far is preliminary; the studies are small, do not have control or placebo groups, or do not compare sauna use to other treatments.
- The research does show some interesting effects, but there has not yet been a strong study showing substantial benefit.
- Manufacturers, bloggers, and members of the popular media exaggerate the magnitude and importance of the results of these small studies and suggest sauna use is more beneficial than it actually has been shown to be.
- Sauna use is probably safe, as long as you stay well hydrated, and may have some benefits. However, you should not expect any real changes.