Scientists Test Whether Sauna Sessions and Heat Therapy Can Improve Mental Health

Hilland, whose research group focuses on neuroimaging and genetics, scanned the scientific literature for the kind of evidence that would support recommending heat as a legitimate intervention for mental health and found very little. "There are many knowledge gaps," she said, though the existing evidence she did find seemed promising. "So we just saw the potential."

The trial is funded by a local municipality. Rather than visiting a windowless research lab, participants take two sessions a week at one of the floating sauna villages that have cropped up in Oslo's inner harbor, a waterfront transformed into a world-class destination for heat-seekers in just the past decade.

Sauna-going, sometimes paired with cold plunges or winter swimming, is attracting a new generation of followers from the United States to Hilland's sauna-steeped Norway. The trend reflects not only the reach of the broader wellness and longevity movement but also a thirst for communal experience and social connection, particularly in the wake of the pandemic.

The science is only beginning to catch up with many of the theorized benefits. Mental health has been considerably less studied than the cardiovascular impact of heat, but it has emerged as one of the more exciting and appealing applications. Large surveys of sauna users reflect what many readily share: psychological benefits more than anything else keep them coming back, whether that is stress reduction, elevated mood, improved sleep or the ineffable post-sauna glow. Some of those self-reported improvements may have less to do with sweating and more to do with the digital detox, time in nature, mindfulness and social connection that sauna-going facilitates. But the weight of the evidence suggests heat itself is also a "powerful physiological stimulus for promoting mental health," said Christopher Lowry, an integrative physiologist and neuroscientist at the University of Colorado, Boulder.

Warm baths were commonplace in psychiatric asylums a century ago, but the modern evidence base largely rests on translational work done with animals and cell models, plus a small number of human studies, most of which lack strict control groups. In his lab, Lowry has explored the physiological mechanisms linking temperature and mental health. When the skin senses heat, those signals travel to a primitive part of the brain that tells the body to cool down, a process that overlaps with a pathway involved in mood and pleasure and implicated in depression. Heat also triggers a specific anti-inflammatory response similar to one that occurs during exercise, a well-established treatment for depression and other mental health conditions. Separately, Lowry said, animal studies find heat activates a group of "serotonin neurons" in the brain that may "provide stress resilience and antidepressant effects."

The strongest human data come from a landmark trial published ten years ago, led by a team at the University of Wisconsin-Madison and co-authored by Lowry. A total of 30 people with depression were randomly separated into two groups. About half spent around two hours in a whole-body infrared machine designed to raise their body temperature to 38.5 C, or about 101 F. The rest received a sham treatment. Within a week, a majority of those in the treatment group had a 50% reduction in their symptoms, and the effects persisted throughout the six-week follow-up period.

Those findings originally inspired Ashley Mason, a clinical psychologist who studies mood disorders and sleep at the University of California, San Francisco, to enter the field. Mason now has funding from the National Institutes of Health and others to study various forms of heat therapy for depression, sleep and loneliness. The renewed scientific interest in using heat for psychiatric conditions partly reflects an intriguing observation: people with depression tend to have difficulty with thermoregulation. "What we know from a bunch of literature is that depressed people seem to run hot," said Mason, also a professor of psychiatry and behavioral science. "When their depression improves, their thermoregulatory system seems to also change." Her lab recently tracked this association.