Deliberate heat exposure for depressive disorders: A systematic review & meta-analysis

Background: Depressive disorders affect approximately 280 million people worldwide and are associated with significant morbidity. Current treatments, including psychotherapy and pharmacotherapy, have limitations in efficacy and tolerability. Deliberate heat exposure (DHE) refers to the controlled exposure to heat through instruments such as saunas, steam showers, or hot baths. DHE has emerged as a potential novel intervention for depressive symptoms. Despite this, no synthesis of the empirical evidence exists. Aims: We conducted a systematic review and meta-analysis of randomised controlled trials (RCTs) investigating DHE’s effects on depressive symptoms. Method: A systematic search strategy was applied to databases (MEDLINE, Scopus, PsycArticles, Cochrane Library) to identify RCTs of DHE for depression published between 1980 and 2025. DHE interventions encompassed infrared whole-body hyperthermia devices, far-infrared ray dry saunas, hyperthermic baths, and balneotherapy. The primary outcome was change in depressive symptoms measured by validated scales. Extracted effects from included studies were pooled using Hedges’ g. Analyses were conducted using the random effects model. Cochrane’s Risk of Bias 2.0 tool was used to assess each RCT’s risk of bias. Results: Seven studies involving 363 participants were included. Random-effects meta-analysis revealed a small but statistically significant effect of DHE in reducing depressive symptoms (Hedges' g = 0.32; 95% CI, 0.12-0.52). Effect sizes ranged from 0.08 to 0.77 across studies. DHE showed greater efficacy when compared to passive controls (g = 0.54; 95% CI, 0.04-1.03) than active controls (g = 0.28; 95% CI, 0.06 to 0.49). Some studies reported rapid onset of improvement within two weeks. DHE was also associated with improvements in sleep quality, pain, and fatigue. Conclusions: DHE demonstrates a small but significant effect in reducing depressive symptoms. Methodological limitations include small sample sizes and intervention heterogeneity, which necessitates larger more rigorous trials to determine a more definitive clinical role for DHE in depression management and determine optimal DHE protocols. While methodological limitations necessitate larger trials to establish definitive protocols, these consistent findings, combined with strong biological plausibility and apparent safety profile, may inform discussions between clinicians and selected patients seeking experimental non-pharmacological approaches.PROSPERO registration (CRD42023471821)