What actually causes depression?
Depression has no single cause. Explore its global footprint below — then dive into 56 evidence-graded causes, the biology that ties them together, and the open research frontier.
Estimated population prevalence of depression. Primary source: WHO Global Health Observatory (GHE 2015), 2015 (185 countries). Greenland & Palestine from GBD/field studies. Cross-country comparisons reflect detection and reporting differences as well as true burden — see Methodology.
The pattern: a convergence funnel
So many different exposures seem to drain into the same downstream biology — chronic neuroinflammation, a dysregulated stress (HPA) axis, and oxidative stress. Smoking, ultra-processed diet, air pollution, metals, microplastics, chronic stress, trauma and poor sleep each plausibly feed this funnel. See the model →
Causal core
Childhood adversity, loneliness, smoking, inactivity, insomnia, inflammation (IL-6), metabolic dysfunction. Evidence →
Robust contributors
Air pollution, ultra-processed food, alcohol, poverty/food insecurity, discrimination, job strain, omega-3 insufficiency.
Emerging frontier
Microplastics in brain tissue, aluminium, blood–brain-barrier leak, metabolic psychiatry. Frontier →
Contested / overstated
Serotonin "imbalance", PFAS, mercury-from-fish, social-media-as-primary-cause. Myths →