You may have heard people talk about chemical imbalances in the brain that occur in depression, suggesting that depression is a medical illness, without psychological causes. However, all psychological problems have some physical manifestations, and all physical illnesses have psychological components as well. In fact, the chemical imbalances that occur during depression usually disappear when you complete psychotherapy for depression, without taking any medications to correct the imbalance. This suggests that the imbalance is the body's physical response to psychological depression, rather than the other way around.
Some types of depression do seem to run in families, suggesting a biological vulnerability. This seems to be the case with bipolar depression and, to a lesser degree, severe major depression. Studies of families, in which members of each generation develop bipolar disorder, found that those with bipolar disorder have a somewhat different genetic makeup than those who are not diagnosed.
However, the reverse is not true. Not everybody with the genetic makeup that causes this vulnerability to bipolar disorder develops the disorder. Additional factors, such as stress and other psychological factors, are involved in its onset as well. Likewise, major depression also seems to occur, generation after generation, in some families, but not with a frequency that suggests clear biological causes. Additionally, it also occurs in people who have no family history of depression. So, while there may be some biological factors that contribute to depression, it is clearly a psychological disorder.
A variety of psychological factors appear to play a role in vulnerability to these severe forms of depression. Most likely, psychological factors are completely responsible for other forms of mild and moderate depression, especially reactive depression. Reactive depression is usually diagnosed as an adjustment disorder during treatment.
People who have low self-esteem, who consistently view themselves and the world with pessimism, or who are readily overwhelmed by stress are more prone to depression. Psychologists often describe social learning factors as being significant in the development of depression, as well as other psychological problems. People learn both adaptive and maladaptive ways of managing stress and responding to life problems within their family, educational, social and work environments. These environmental factors influence psychological development, and the way people try to resolve problems when they occur. Social learning factors also explain why psychological problems appear to occur more often in family members, from generation to generation. If a child grows up in a pessimistic environment, in which discouragement is common and encouragement is rare, that child will develop a vulnerability to depression as well.
A serious loss, chronic illness, relationship problems, work stress, family crisis, financial setback, or any unwelcome life change can trigger a depressive episode. Very often, a combination of biological, psychological, and environmental factors are involved in the development of depressive disorders, as well as other psychological problems. When you feel depressed, and don't know where to turn, talk to someone who can help.... a psychologist.