What the research shows

If you've walked out of a sauna feeling inexplicably lighter, that mood lift may have a more interesting explanation than simply "warmth is nice." A growing body of clinical research suggests that deliberate heat exposure, and infrared sauna therapy in particular, may offer genuine relief for people living with depression. The science is still in its early stages, but the results so far are striking enough to take seriously.

Why this matters in Britain

Mental health in the UK is under enormous strain. According to the latest Adult Psychiatric Morbidity Survey (2023/24), around 1 in 5 people in England report experiencing a common mental health problem - such as depression or anxiety - in any given week. The NHS received 5.2 million mental health referrals in 2024, up nearly 38% compared to 2019. While talking therapy and antidepressants remain the frontline treatments, demand consistently outstrips capacity. That pressure is driving genuine scientific interest in complementary approaches - and heat therapy is emerging as one of the more credible candidates.

What the UCSF trials actually found

The most significant work in this area comes from Dr Ashley Mason, a clinical psychologist at the UCSF Osher Center for Integrative Health. Her team's 2024 study - the first to formally combine infrared sauna sessions with psychotherapy for major depressive disorder (MDD) - enrolled 16 adults and put them through eight weekly sessions of cognitive behavioural therapy (CBT), alongside four sessions of whole-body heat treatment, conducted in an infrared sauna dome.

The results were notable. Of the 12 participants who completed the programme, 11 no longer met the diagnostic criteria for major depressive disorder at the end of the study. Dr Mason described the symptom reductions as "much higher than we would have expected from CBT alone without heat treatment."

A 2025 follow-up, this time using a randomised design - 30 participants with MDD, half receiving real heat sessions and half a sham version - produced similarly encouraging numbers: 86.2% of those who completed the programme no longer met criteria for MDD at their final assessment.

It's important to be clear about what this evidence is and isn't. These are small pilot studies designed to test whether the approach is feasible and acceptable to patients, not large-scale trials proving causation. Dr Mason herself has been explicit: "It is early days." Larger randomised controlled trials are planned, and they will take years. The numbers are promising - not definitive.

The surprising science

One of the more counterintuitive findings underpinning this research comes from a separate large UCSF study, published in 2024, involving over 20,000 participants across 106 countries. It found that people with depression consistently run at a higher body temperature than those without - and crucially, the relationship appears dose-dependent: the more severe the depression, the higher the body temperature.

The hypothesis that follows is almost paradoxical. Heating the body deliberately in a sauna causes it to work hard to cool down. After the session ends, core body temperature continues to decrease - and may drop lower, and stay lower for longer, than if you had tried to cool the body directly. For people whose systems are running chronically hot, that rebound cooling effect may be part of what's driving the mood improvement.

Researchers also believe that thermosensory pathways - the neural systems that relay heat signals from skin to brain - may act as gateways to mood regulation.

What about the ice bath trend?

Given the widespread interest in cold-water immersion, it's worth asking whether the mood benefits simply come from any dramatic temperature shift, regardless of direction. Gifford, whose book Hotwired draws together the research on heat and health, concludes that the evidence for heat currently looks more robust than for cold — a view shared by the UCSF researchers, who note that the clinical data on heat therapy for depression is more developed and mechanistically coherent than that around cold exposure.