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Environmental

Adverse childhood experiences (incorporating childhood abuse, neglect and family dysfunction) markedly increase the risk of major depression, especially if more than one type. Childhood trauma also correlates with severity of depression, poor responsiveness to treatment and length of illness. Some are more susceptible than others to developing mental illness such as depression after trauma, and various genes have been suggested to control susceptibility. Couples in unhappy marriages have a higher risk of developing clinical depression.

There appears to be a link between air pollution and depression and suicide. There may be an association between long-term PM2.5 exposure and depression, and a possible association between short-term PM10 exposure and suicide.