It is natural to feel sad, down or blue at times, but depression is a serious mental health condition that affects a person’s ability to fully participate in daily activities. A person with depression may experience persistent sad mood, feelings of emptiness, hopelessness or worthlessness, loss of interest or pleasure in activities or suicidal thoughts. There is no single cause of depression. Contributing factors may include family history of depression, a significant life change, such as a birth or a loss, trauma or a medical condition.