Infrared Saunas and Cortisol: What the Research Actually Shows

Infrared saunas are commonly advertised as one of the more effective ways to lower cortisol and reset a stressed nervous system, often positioned as a gentler alternative to traditional high-heat saunas because their infrared panels heat the body more directly at lower ambient temperatures. The stress-relief pitch is plausible on its face, but the research specifically measuring cortisol before and after infrared sauna sessions is newer, and more mixed, than the marketing suggests.

The proposed mechanism is heat-induced activation of the parasympathetic nervous system, the body's rest-and-digest counterpart to the fight-or-flight response, which in theory should follow a warm, passive heat exposure once a session ends. This is a reasonable extension of what is already known about heat therapy generally: Mayo Clinic notes that regular sauna use, infrared or traditional, is associated with cardiovascular benefits that resemble those of light aerobic exercise, and Cleveland Clinic considers heat therapy an established way to ease muscle stiffness and improve short-term joint mobility. Cortisol specifically, though, is a narrower and less settled question, and it is where the strongest marketing claims tend to outrun the actual data.

One of the more direct pieces of evidence comes from a 2025 study in the journal Temperature, in which researchers at the University of Jyvaskyla tracked 40 female team-sport athletes using post-exercise infrared sauna sessions across a six-week training block. The results were more complicated than a simple before-and-after drop in cortisol: in the first week, cortisol actually rose the morning after sauna sessions, suggesting an added physiological stress from the heat exposure layered on top of exercise. By the sixth week, that response had essentially reversed, with the researchers describing an adaptation in which both cortisol and autonomic nervous system responses settled down with repeated exposure.

That finding complicates the common claim that a sauna session reliably and immediately lowers cortisol. In this study, the opposite happened at first, and the calming effect only emerged after weeks of consistent use, not from a single visit. It is a useful example of how a real physiological process, adaptation to repeated heat stress, gets simplified into a much cleaner-sounding marketing claim, instant relaxation and lower stress hormones after one session, than the underlying data actually shows.

Separately, "detox" language attached to infrared saunas, the idea that sweating meaningfully clears cortisol, toxins, or other unwanted substances from the body, is not well supported. Sweat is overwhelmingly water, sodium, and other electrolytes; the liver and kidneys, not skin, do the vast majority of the body's clearance work. That does not make infrared sauna use useless, but it is a separate, weaker claim than the more plausible relaxation and cardiovascular benefits described above, and the two are worth evaluating on their own terms.

The most defensible way to think about infrared sauna and cortisol, based on current evidence, is that regular use over time is reasonably linked to relaxation and some cardiovascular benefits similar to light exercise, while the specific claim of a fast, reliable single-session cortisol drop is thinner than advertised and, in at least one recent study, briefly moved in the opposite direction before adapting over several weeks.