The mechanisms underlying the effects of heat on mental health: A narrative review

While recent studies have advanced our understanding of how heat affects mental health, the underlying mechanisms of this relationship remain fragmented. Previous reviews have emphasized broad and general physiological, psychological, behavioural, and social pathways, often neglecting the heterogeneity of mental disorders in terms of vulnerability and outcomes. We conducted a narrative review to tackle this gap and propose an outcome-oriented framework to better integrate evidence on heat-related mental health risks. We searched PubMed and Google Scholar from January 2023 to September 2025 and conducted backward citation tracking of relevant reviews and primary studies, with no restrictions on publication language, date, or article type. The review focuses on two distinct yet interrelated pathophysiological-related outcomes: (1) exacerbation of pre-existing mental health disorders, and (2) heat-related illnesses such as heat exhaustion and heat stroke. Moreover, we integrated these pathways to six psychiatric conditions most established as heat sensitive: organic disorders (International Classification of Diseases-10 th Edition F00-F09), substance misuse (F10-F19), schizophrenia (F20-F29), bipolar disorders (F31), neurotic disorders (F40-F49), and suicidal behaviour (X60-X84). First, our findings show that heat exposure can exacerbate symptoms in individuals with schizophrenia, bipolar disorder, anxiety disorders, and suicidal behaviour. Key mechanisms include (i) neurotransmitter imbalances, (ii) physiological stress, and (iii) sleep disruption. Second, heat exposure can contribute to heat-related illnesses, particularly among individuals with organic disorders, substance misuse, schizophrenia, and bipolar disorder due to (i) ineffective thermoregulatory behaviours, (ii) impaired neuropathways, and (iii) interactions with psychotropic medications or substances. By mapping outcome- and diagnosis-specific pathways, this review offers a more integrated understanding of how heat impacts mental health. This approach may help clinicians anticipate exacerbations and guide tailored interventions. It also provides a conceptual basis for future, precise, mechanism-driven research questions and for policymakers to design targeted adaptation strategies in public health.