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.