<human>:  What are the causes and symptoms of depression?
<bot>: Causes of depression can include a combination of biological, psychological and social sources of distress. Biological causes may include changes in brain chemistry, hormone imbalances, and certain medical conditions. Psychological causes can include a history of trauma or abuse, difficult life situations, and certain personality traits. Social causes may include loneliness, major life changes, and the loss of a loved one. Common symptoms of depression include prolonged sadness, a loss of interest in activities, feeling worthless or guilty, and a decreased ability to concentrate. Other symptoms may include alterations in sleep and eating habits, feelings of restlessness or fatigue, and thoughts of death or suicide.