“Sauna treats depression.”

The research found this

The strongest trial randomized 34 adults with major depression who were taking no psychiatric drugs to one session of whole-body hyperthermia or a sham session.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 ran 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 ↗ The sham lasted just as long with the 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 the gap was 4.27 points and still statistically significant, and it held 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 ↗ In a later analysis of the same trial, people whose IL-6 signaling rose more right after the session had lower depression scores over the following 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-type 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 sat at about 57.2°C until rectal temperature reached 38.5°C or 140 minutes passed, and the others had 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 which arm they were in. In an older randomized trial of Waon infrared sauna in 28 mildly depressed inpatients, the treated group reported fewer physical complaints and better appetite than the untreated group, and 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. In Boston, 80 adults with moderate to severe depression were randomized to Bikram yoga in a 40.6°C room or a waitlist, and 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 can't be separated from the exercise. In a trial of 53 women with depression, Bikram yoga and aerobic exercise produced nearly identical response rates of 61.1% and 60.0%, and both 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 ↗

Hot baths and the Finnish cohort add weaker evidence. Twice-weekly 40°C baths beat an exercise program by 4.3 points on the Hamilton scale at two weeks in a German pilot of 45 outpatients, 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 ↗ Finnish men who took four to seven saunas a week developed psychotic disorders at 2.8 per 1,000 person-years, against 8.1 in once-a-week bathers, and that outcome included psychoses due to 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 ↗