Lack of reliable evidence supporting the claim that sauna bathing is an effective way to “detox” the body

Social media posts on Facebook and Instagram have touted the benefits of sauna bathing, receiving tens of thousands of views altogether. For example, this Facebook reel shows Raymond Francis, the author of a series of health books, claiming sauna bathing is “the only reliable way” to get rid of “terrible chemicals” in the body.

Similarly, this Instagram post claimed sweating is “one of your body’s most effective ways to expel harmful substances” including heavy metals and toxic human-made chemicals.

This idea isn’t new, as these articles from National Geographic and PBS can attest to. However, there’s little evidence supporting the idea that sauna bathing “detoxes” the body by inducing sweating. We explain more below.

Sauna is associated with physical and mental health benefits

Sauna culture originated in Finland, but the practice of passive heat therapy in general—which includes hot spring bathing and Native American sweat lodges—can be found all over the world.

Various types of saunas exist: for example, in traditional saunas, a room is heated using wood in a fireplace. Modern saunas, on the other hand, use infrared radiation or electricity to generate heat in a room. Temperatures in a typical Finnish sauna can range from 80 to 100 degrees Celsius, although some may use even higher temperatures.

There is scientific evidence indicating that sauna bathing can improve physical health. Science Feedback reached out to Jari Laukkanen, a cardiologist and professor at the University of Eastern Finland, who has investigated the health effects of sauna.

In an email, Laukkanen stated that “there is accumulating research evidence that regular sauna bathing improves health”. Among the evidence, he cited a 2018 review of the scientific literature which reported that sauna bathing is associated with reduced risk of cardiovascular disease^[1], as well as a 2023 review, which found that sauna bathing enhanced improvements in blood pressure and cholesterol level following exercise^[2]. [Disclosure: Both reviews were co-authored by Laukkanen.]

However, there’s currently little evidence supporting the idea that sauna bathing is an effective way to “detox” the body by inducing sweating. “More studies on sauna and toxins would be needed,” said Laukkanen.

Certain toxins are excreted in sweat, but it’s unclear if quantities are biologically meaningful

Humans have different sweat glands for different functions. When it comes to sweating as a result of heat or exercise, eccrine sweat glands play the main role. Sweating in these contexts helps cool our body through evaporative heat loss. Apocrine sweat glands, on the other hand, are activated by hormonal stimulation during puberty and thus only begin to function after this occurs. They’re involved in emotional sweating, such as in response to fear or pain.

More than 99 percent of sweat is water. Salt, lactate, and antibodies are among the rest of the components. But that’s not all. Studies have also reported small quantities of heavy metals and other toxic compounds in sweat.

A 2011 study by Genuis et al. tested the amount of 18 metals including lead, arsenic, and mercury in the blood, urine, and sweat. The study was relatively small, testing these levels in just 20 people—ten healthy individuals, and ten with various health problems^[3].

Urine and blood samples were collected once from each participant. Study participants collected their own sweat samples “by placing the jar against their prewashed skin when actively sweating or by using a stainless steel spatula against their skin to transfer perspiration directly into the glass jar”.

The authors reported the presence of all 18 metals in the majority of the sweat samples collected. Interestingly, they also found that some of these metals were present in greater amounts in sweat compared to urine, suggesting that these metals were better excreted in sweat than in urine.

A 2015 study by Porucznik et al. measured the amount of bisphenol A (BPA)—a chemical used to make certain plastics that is now a public health concern—in urine and sweat^[4]. Sweat was collected using sweat patches worn by participants for one week, while urine samples were collected every day of the week.

The authors detected BPA in 340 out of 386 urine samples collected, but BPA was detected in only three sweat patches. These results indicate that while BPA could be excreted in sweat, the amount is much smaller than that excreted in urine.

However, there are methodological limitations that raise the question of how reliable the results are.

A 2019 review evaluating studies of eccrine sweat composition^[5] pointed out that many studies, including the one by Genuis et al. mentioned above^[3], collected sweat in ways that are prone to contamination. For example, in the study by Genuis et al., participants could use scraping to collect their sweat. The review pointed out the problem with this:

“With these methods, it is probable that sweat samples were tainted with sebum secretions. Scraping methods increase the likelihood of skin surface (epidermal cells) contamination because scraped sweat contains 4 – 10x more lipid than clean sweat; potentially explaining the high concentrations of some the of[sic] lipophilic toxicants in sweat.”

In other words, when sweat is collected by scraping, the sweat sample is likely to contain more than just sweat: skin cells and sebum can also end up in the sample, which could artificially increase the level of certain toxins in the sample. As such, the review concluded that “direct evidence for sweating as an effective detoxification method is lacking”.

A letter by Laukkanen and colleagues, published in the Mayo Clinic Proceedings in 2019, highlighted the research gap with regards to toxin excretion in sweat:

“[I]t is not known […] if sauna bathing helps to get rid of toxins, as the liver and kidneys usually remove more toxins than sweat glands. It is also unclear whether the minuscule amount of toxins in sweat actually indicates a health concern. In addition, the concentrations of metals or other toxins detected in sweat are quite low. Whether sauna bathing will be a useful strategy for the elimination of toxins, including organochlorinated pesticides, from the body is a topic for further investigation.”

Speaking to National Geographic, Pascal Imbeault, a professor at the University of Ottawa who studies how exposure to persistent organic pollutants can influence health, stated that the amount of these chemicals in sweat is so low that they are “essentially meaningless”. Specifically:

“Imbeault and his colleagues found that a typical person doing 45 minutes of high-intensity exercise could sweat a total of two liters in a day—normal background perspiration included—and all that sweat would contain less than one-tenth of a nanogram of these pollutants.”

Similarly, Angela Lamb, a dermatologist at Mount Sinai, told PBS that the amount of heavy metals and BPA excreted in sweat is so small it doesn’t make much difference to their removal from the body.

In summary, while some studies showed that certain heavy metals and chemicals are excreted in sweat, there’s a lack of evidence showing that their excretion in sweat is biologically meaningful or makes a difference to health.

“Detox” is generally unnecessary for people with functioning liver and kidneys

Detoxification is a genuine medical procedure used in cases of poisoning. One example is chelation therapy, which is used for heavy metal poisoning.

However, the term “detox” is popularly used to refer to the practice of removing typically ill-defined “toxins” that allegedly cause all kinds of medical conditions ranging from lung problems to cancer. Various regimens, ranging from enemas to juice-only diets to dietary supplements, are promoted for the purpose of “detox” and “cleansing”.

However, there’s no evidence that such regimens are effective or even necessary, since the liver and kidneys do the heavy lifting when it comes to removing harmful substances from our bodies. While some people report feeling better after a “cleanse”, this could simply be due to a person improving their eating habits, like reducing the amount of unhealthy food they consume, rather than toxin removal.

“If someone who maybe has been eating a lot of refined food, not a lot of fiber, minimal fruits and vegetables, and now they’re replacing those foods, even in smaller amounts, with nutrient-dense foods, of course they’re going to feel better,” Melissa Prest, a nutritionist and spokesperson for the Academy of Nutrition and Dietetics, told National Geographic.

This video co-produced by the American Chemical Society explained that the liver contains enzymes for detoxification and the kidneys filter waste from the blood. “As long as you’re otherwise healthy, your body’s natural detox processes are incredible at what they do,” toxicologist Raychelle Burkes stated in the video.

Sauna bathing is distinct from typical “detox” regimens in that scientific evidence does show it’s associated with health benefits. However, it’s also important to consider some caveats. Certain groups of people, such as those with uncontrolled high blood pressure and heart disease, should seek medical advice before using a sauna.

Additionally, it’s important to practice sauna bathing in moderation. Harvard Health recommends that people limit the duration of sauna bathing to between 15 to 20 minutes, and to drink plenty of water after a sauna session to replace the water lost from sweating.

Conclusion

Scientific evidence indicates that sauna bathing is linked to various health benefits, particularly for the cardiovascular system. However, there’s currently a lack of reliable evidence supporting the claim that sweating from sauna bathing is an effective way to remove toxins from the body. It’s generally unnecessary to “detox” our body, since the liver and kidneys already perform this function effectively.

REFERENCES

• 1 – Laukkanen et al. (2018) Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence. Mayo Clinic Proceedings.
• 2 – Kunutsor and Laukkanen. (2023) Does the Combination of Finnish Sauna Bathing and Other Lifestyle Factors Confer Additional Health Benefits? A Review of the Evidence. Mayo Clinic Proceedings.
• 3 – Genuis et al. (2011) Blood, urine, and sweat (BUS) study: monitoring and elimination of bioaccumulated toxic elements. Archives of Environmental Contamination and Toxicology.
• 4 – Porucznik et al. (2015) A Preliminary Study of Biomonitoring for Bisphenol-A in Human Sweat. Analytical Toxicology.
• 5 – Baker LB. (2019) Physiology of sweat gland function: The roles of sweating and sweat composition in human health. Temperature.
• 6 – Laukkanen and Kunutsor. (2024) The multifaceted benefits of passive heat therapies for extending the healthspan: A comprehensive review with a focus on Finnish sauna. Temperature.