The biopsychosocial model describes the linkage of depression causes. The diathesis-stress model talks about the relationship between potential causes of depression and the amount that people may be sensitive or vulnerable to react to those causes. The diathesis-stress model believes that people have different levels of sensitivity for developing depression. In the language of this model, these sensitivities are referred to as diatheses. Diatheses include some of the biological and psychological factors mentioned in the discussion of the biopsychosocial model. Some people may have more of these factors for developing depression than other people. This model suggests that having a sensitivity towards developing depression by itself is not enough to cause the condition. Instead, a person's sensitivities must interact with stressful life events, which can be social, psychological or biological, in order to lead to the condition.
According to this model, the greater a person's sensitivity for developing depression, the less environmental stress is needed to cause him or her to become depressed. If someone has a smaller amount of sensitivity for becoming depressed, it will take higher levels of stress for the condition to happen. Until this critical amount of stress has been reached, people will generally live their lives normally. Their sensitivity is considered to be hidden.
The impact of stressful events is different for each person. Death or other losses such as a job layoff; relationship difficulties like divorce; normal milestones such as puberty, marriage, or retirement; alcoholism or drug abuse; neurochemical and hormonal imbalances; and infections can all be powerful enough to cause depressive symptoms in someone with a sensitivity for this illness. However, each of these events will impact people in a unique way. A significant loss may be enough to trigger depression in one person, but a very similar loss experienced by another person might not cause much of a reaction at all.
According to both the Biopsychosocial Model and the Diathesis-Stress Theory, depressive disorders are caused by many psychological, social, and biological factors. These factors interact with one another, but are also affected by a person's unique sensitivities. Depression is a very complex condition that needs to be thought about in an integrated way. This is known as a holistic approach. Since no one factor causes depression, it is unreasonable to expect that only one type of treatment can fix the problem. Also what works for one person may not work for another in terms of treatment.