Sauna for Mental Health: Depression and Anxiety (2026)

The trial that brought sauna into mainstream psychiatry research is Janssen and colleagues' 'Whole-Body Hyperthermia for the Treatment of Major Depressive Disorder', published in JAMA Psychiatry in 2016.

Design:

• Randomised controlled trial.
• 34 patients with moderate to severe major depressive disorder, randomised to whole-body hyperthermia via infrared chamber or sham-control mild heat .
• Active arm: a single infrared chamber session, until rectal temperature reached 38.6°C (101.5°F), with an average duration of 47 minutes to reach target and a further 60 minutes of rest in the chamber.
• Follow-up at 1, 2, 4 and 6 weeks post-intervention.

Headline finding: a single whole-body hyperthermia session produced an antidepressant effect that lasted six weeks, with a Cohen's d effect size of 2.23. For comparison, typical pharmaceutical antidepressant trials produce Cohen's d in the 0.3 to 0.5 range. 2.23 is exceptionally large and was the finding that put sauna on the psychiatric research radar.

Caveats worth knowing: the sample size is small (34 total), the intervention was infrared chamber rather than traditional Finnish sauna, the sham-control did receive some heat, and the trial has not yet been replicated at meaningful scale. A subsequent CBT-plus-hyperthermia combination trial extended the work but the field still needs the large-cohort replication that the Janssen finding implicitly demands.

Hussain and Cohen's 2018 clinical review pulled together the wider evidence across sauna and mental health outcomes. The review's main observations:

• Lower resting cortisol in regular sauna users compared with non-users in comparable lifestyle studies. Cortisol is the headline stress hormone and lower resting levels are a credible marker of reduced chronic stress load.
• Improved heart rate variability (HRV). Regular sauna users show increased parasympathetic tone - the 'rest and digest' branch of the autonomic nervous system - measured via HRV. Higher HRV is associated with better emotional regulation, lower baseline anxiety, and faster recovery from acute stressors.
• Lower self-reported anxiety and depression scores in regular sauna users across multiple smaller observational studies.
• Improved sleep quality in users who sauna in the early evening - the post-sauna core temperature drop matches the natural circadian temperature dip that signals sleep onset.

The Hussain and Cohen review's honest caveat: most of the supporting evidence is observational rather than randomised, and many of the studies have small sample sizes. The review describes the evidence base as promising and consistent rather than definitive.

Three mechanism stories are best supported by current evidence:

• Autonomic shift. Sauna heat triggers a sympathetic surge followed by a parasympathetic rebound in the rest phase. Repeated exposure shifts resting balance toward parasympathetic dominance, which translates to lower resting cortisol, higher HRV, and better stress recovery. This is the cleanest mechanistic story.
• BDNF (brain-derived neurotrophic factor). Heat exposure increases BDNF levels in animal and limited human studies. One controlled human study showed BDNF rose by around 66 percent for the 15 minutes following whole-body hyperthermia to 39.5°C via hot water bath. BDNF is the proposed mechanism for the lasting antidepressant effect in the Janssen trial - BDNF mediates synaptic plasticity, and many effective antidepressants increase BDNF via different routes.
• Heat shock protein response. The same HSP70 response that protects cellular machinery in the cardiovascular story also operates in neural tissue. The neuroprotective angle is more speculative but is the proposed bridge between the sauna literature and the dementia outcomes in the KIHD cohort.

One mechanism worth being careful about: the 'endorphin high' narrative often cited for sauna is poorly supported by direct measurement. The autonomic-shift story is better supported and probably explains most of the post-sauna mood lift.

The sauna and mental health story is interesting but should be read with proper calibration.

What the evidence supports:

• The 2016 Janssen RCT is a real result and the effect size is genuinely large for a psychiatric trial.
• The autonomic-shift, HRV and cortisol findings are well replicated across multiple smaller studies.
• Mechanistic plausibility via BDNF and HSP70 is reasonable.
• Sauna is unlikely to harm mental health in users without specific contraindications.

What the evidence does not yet support:

• Sauna as a replacement for evidence-based depression treatment. The Janssen trial is one small RCT. Antidepressant medication and evidence-based psychotherapy (CBT, IPT) have decades of larger trials behind them. Sauna may complement these but should not replace them for clinical depression.
• A specific 'dose' for mental health. The Janssen trial used a single high-intensity infrared session to 38.5°C core temperature, which is not the same as a regular 70 to 90°C Finnish sauna routine. The optimal sauna routine for mental health specifically is not yet established.
• Generalisation to severe or treatment-resistant depression. The Janssen trial population was moderately to severely depressed but did not specifically test treatment-resistant cases. Severe or refractory depression needs psychiatric input.
• Anxiety-disorder-specific evidence. The strongest trial data is on depression rather than anxiety. The anxiety story is mostly observational and via HRV / cortisol mechanisms rather than direct trial evidence.

Translating the evidence into a practical UK protocol for general mental wellbeing - not as treatment for diagnosed depression or anxiety:

• Frequency: 2 to 4 sessions per week is the routine the broader evidence supports. Daily sauna is not necessary for the mental-wellbeing benefit and may not be sustainable for most UK lifestyles.
• Duration: 15 to 20 minutes per round at 70 to 90°C. Multi-round sessions (2 to 3 cycles with cold immersion and warm rest) suit the cardiovascular and contrast-bathing literature; single-round longer sessions may better match the Janssen-style antidepressant route but no direct comparison study exists.
• Timing: early evening sauna (2 to 3 hours before sleep) suits the sleep-and-mood story best, as the post-sauna core-temperature drop aligns with circadian sleep onset.
• Combine with the existing standard of care. If you are already taking antidepressant medication or in psychotherapy for depression or anxiety, treat sauna as a complementary lifestyle factor - useful but additional, not instead of.
• Get clinical input for severe symptoms. Sustained low mood, anhedonia, suicidal thoughts, severe anxiety - these need GP or specialist involvement, not a sauna routine on its own.