Genetic Factors

There is a risk for developing depression when there is a family history of the illness, indicating that a biological vulnerability may be inherited. The risk is somewhat higher for those with bipolar disorder. However, not everybody with a family history develops the illness. In addition, major depression can occur in people who have had no family members with the illness. This suggests that additional factors, possibly biochemistry, environmental stressors, and other psychosocial factors, are involved in the onset of depression.

Biochemical Factors

Evidence indicates that brain biochemistry is a significant factor in depressive disorders. It is known, for example, that individuals with major depressive illness typically have dysregulation of certain brain chemicals, called neurotransmitters. Additionally, sleep patterns, which are biochemically influenced, are typically different in people with depressive disorders. Depression can be induced or alleviated with certain medications, and some hormones have mood-altering properties. What is not yet known is whether the "biochemical disturbances" of depression are of genetic origin, or are secondary to stress, trauma, physical illness, or some other environmental condition.

Environmental and Other Stressors

Significant loss, a difficult relationship, financial problems, or a major change in life pattern have all been cited as contributors to depressive illness. Sometimes the onset of depression is associated with acute or chronic physical illness. In addition, some form of substance abuse disorder occurs in about one-third of people with any type of depressive disorder.⁷

Other Psychological and Social Factors

Persons with certain characteristics-pessimistic thinking, low self-esteem, a sense of having little control over life events, and a tendency to worry excessively-are more likely to develop depression. These attributes may heighten the effect of stressful events or interfere with taking action to cope with them or with getting well. Upbringing or sex role expectations may contribute to the development of these traits. It appears that negative thinking patterns typically develop in childhood or adolescence. Some experts have suggested that the traditional upbringing of girls might foster these traits and may be a factor in women's higher rate of depression.