Claim Check: "Sweating in a Sauna or Hot Bath Detoxes the Body"

What the claim says

The claim is usually that heat makes you sweat, and that sweat carries "toxins" out of the body. "Toxin" is rarely defined. A claim worth checking names the substance, the amount removed, and a health benefit that followed.

What studies found about sweat

• Toxic metals in sweat. A 2012 systematic review looked for arsenic, cadmium, lead and mercury in sweat. Of 122 records found, 24 were included [1]. The authors note that populations, sweat collection methods and concentrations varied widely [1]. They concluded that sweating deserves consideration for toxic element detoxification, and that appropriately sized trials are needed [1]. One finding was a case report in which mercury levels normalized with repeated saunas [1].
• A small comparison study. A 2011 study collected blood, urine and sweat from 20 people, 10 healthy and 10 with various health problems [2]. The authors reported that induced sweating appears to be a potential method for elimination of many toxic elements [2].

How to read this: these are small, mixed groups, not trials that compared sauna or bath users with a control group on health outcomes. Finding a substance in sweat does not show that the body is better off. We did not find, in what we read, evidence of the amount removed compared with what the kidneys remove, or of a health benefit. Proper evidence not found for that comparison; we searched PubMed for sweat, sauna and detoxification reviews.

What the kidneys do

NIDDK says your kidneys remove wastes and extra fluid from your body [3]. A sauna or bath is not described there as part of that job. We did not read a source that compares the amount removed by sweating with the amount removed by the kidneys.

What reviews of sauna and "detox" say

• A systematic review of regular dry sauna bathing says many health benefits are claimed, but the medical evidence to support these claims is not well established [4]. It found 40 clinical studies; only 13 were randomized trials and most were small [4].
• NCCIH says a 2015 review found no compelling research that "detox" diets eliminate toxins from the body [5]. That page is about diets and cleanses, so it supports only the general point that detox marketing often lacks evidence [5].

Where to read more

• Claim Check: "Detoxifies the Body" covers the wider claim.
• Sauna: evidence summary and infrared sauna cover sauna studies.
• Temperature exposure safety covers heat and cold risks.
• Red flags in hydrotherapy marketing and detox foot baths.