“Sauna treats depression.”

The research found this

The strongest trial randomly assigned 34 adults with major depression who were taking no psychiatric drugs to one session of whole-body hyperthermia or a sham.1Source 1 · Randomized trialWhole-Body Hyperthermia for the Treatment of Major Depressive DisorderJanssen CW, Lowry CA, Mehl MR, et al.. JAMA Psychiatry, 2016.Read the paper ↗PubMed ↗ The heat came from a medical device with infrared lamps over the chest and heating coils over the legs. It stayed on until core temperature reached 38.5°C, and an hour of cooling followed.2Source 2 · Clinical trialThe antidepressant effect of whole-body hyperthermia is associated with the classical interleukin-6 signaling pathwayMac Giollabhui N, Lowry CA, Nyer M, et al.. Brain, Behavior, and Immunity, 2024.Read the paper ↗PubMed ↗ For the sham, the device ran for the same length of time with its main lamps switched off.

Among the 29 people analyzed, the heated group scored 6.53 points lower than the sham group on the Hamilton depression scale a week later. At week 6 they were still 4.27 points lower, and the difference stayed statistically significant after the researchers adjusted for what people expected.1Source 1 · Randomized trialWhole-Body Hyperthermia for the Treatment of Major Depressive DisorderJanssen CW, Lowry CA, Mehl MR, et al.. JAMA Psychiatry, 2016.Read the paper ↗PubMed ↗ A later analysis of the same trial tracked the inflammatory messenger IL-6. People whose IL-6 signaling rose more right after the session had lower depression scores over the next six weeks.2Source 2 · Clinical trialThe antidepressant effect of whole-body hyperthermia is associated with the classical interleukin-6 signaling pathwayMac Giollabhui N, Lowry CA, Nyer M, et al.. Brain, Behavior, and Immunity, 2024.Read the paper ↗PubMed ↗

Trials that used sauna-style heat are less clear. A pilot at the University of California, San Francisco gave 30 adults with major depression eight weekly sessions of cognitive behavioral therapy plus four sessions in an infrared sauna dome.3Source 3 · Randomized trialA Randomized Trial Testing a Novel Mind and Body Intervention for Depression: Cognitive Behavioral Therapy (CBT) and Whole-Body Hyperthermia (WBH)Mason AE, Hartogensis W, Chowdhary A, et al.. Global Advances in Integrative Medicine and Health, 2025.Read the paper ↗PubMed ↗ Half of them got heat at about 57.2°C until rectal temperature reached 38.5°C or 140 minutes passed, and the others got a sham at about 46.0°C. Depression scores fell 19.07 points with heat and 21.10 with sham, and every person in the heat group guessed they'd had the heat treatment. An older randomized trial tested the Japanese infrared sauna routine called Waon therapy on 28 mildly depressed inpatients. Compared with the untreated group, the treated group reported fewer physical complaints and a better appetite, and their mental complaints only trended lower.4Source 4 · Randomized trialRepeated Thermal Therapy Diminishes Appetite Loss and Subjective Complaints in Mildly Depressed PatientsMasuda A, Nakazato M, Kihara T, et al.. Psychosomatic Medicine, 2005.Read the paper ↗PubMed ↗

Heated yoga has the largest trial. Researchers in Boston randomly assigned 80 adults with moderate to severe depression to Bikram yoga in a 40.6°C room or to a waitlist. After eight weeks, 59.3% of the yoga group had improved by at least half, against 6.3% of the waitlist.5Source 5 · Randomized trialA Randomized Controlled Trial of Community-Delivered Heated Hatha Yoga for Moderate-to-Severe DepressionNyer MB, Hopkins LB, Nagaswami M, et al.. The Journal of Clinical Psychiatry, 2023.Read the paper ↗PubMed ↗ The heat in a yoga class can't be separated from the exercise. In a trial of 53 women with depression, 61.1% responded to Bikram yoga and 60.0% to aerobic exercise, and both groups far outpaced a waitlist.6Source 6 · Randomized trialRandomized controlled trial of bikram yoga and aerobic exercise for depression in women: Efficacy and stress-based mechanismsLa Rocque CL, Mazurka R, Stuckless TJ, et al.. Journal of Affective Disorders, 2021.Read the paper ↗PubMed ↗

The evidence from hot baths and Finnish sauna habits is weaker. In a German pilot of 45 outpatients, twice-weekly baths at 40°C beat an exercise program by 4.3 points on the Hamilton scale at two weeks, although 13 of the 23 people assigned to exercise dropped out.7Source 7 · Randomized trialEffects and feasibility of hyperthermic baths in comparison to exercise as add-on treatment to usual care in depression: a randomised, controlled pilot studyNaumann J, Kruza I, Denkel L, et al.. BMC Psychiatry, 2020.Read the paper ↗PubMed ↗ A Finnish study that followed men for years found fewer psychotic disorders in frequent bathers. Men who took four to seven saunas a week developed them at 2.8 cases per 1,000 men per year, against 8.1 in once-a-week bathers. That count included psychoses caused by memory disorders such as Alzheimer's disease.8Source 8 · Cohort studySauna Bathing and Risk of Psychotic Disorders: A Prospective Cohort StudyLaukkanen T, Laukkanen JA, Kunutsor SK. Medical Principles and Practice, 2018.Read the paper ↗PubMed ↗