Depression is a common and serious mental health condition that affects how a person feels, thinks, and acts. It can cause persistent feelings of sadness, loss of interest, hopelessness, and low self-esteem. Depression can also interfere with daily functioning, such as work, school, social activities, and relationships. Depression is not a sign of weakness or a character flaw. It is a treatable illness that can be caused by a combination of biological, psychological, and environmental factors. Depression can affect anyone, regardless of age, gender, race, or background.