What is depression and what can I do about it? By Laura Goldman Sadness, feeling down and having a loss of interest or pleasure in daily activities are familiar feelings for all of us. But if they persist and affect our lives substantially, the issue may be depression. Depression is the main cause of disability worldwide, according to the World Health Organization (WHO). It can affect adults, adolescents, and children. In this article, learn what depression is and what causes it. We also describe the types, their treatments, and more. Definition A person with depression may experience persistent sadness. Depression is a mood disorder that involves a persistent feeling of sadness and loss of interest. It is different from the mood fluctuations that people regularly experience as a part of life. Major life events, such as bereavement or the loss of a job, can lead to depression. However, doctors only consider feelings of grief to be part of de