Definition of Major depression:

Major depression is when five or more symptoms of depression are present for at least 2 weeks. These symptoms include feeling sad, hopeless, worthless, or pessimistic. In addition, people with major depression often have behavior changes, such as new eating and sleeping patterns. Major depression increases a person's risk of suicide.

Causes, incidence, and risk factors:

The exact cause of depression is not known. Many researchers believe it is caused by chemical imbalances in the brain, which may be hereditary or caused by events in a person's life.

Some types of depression seem to run in families, but depression can also occur in people who have no family history of the illness. Stressful life changes or events can trigger depression in some people. Usually, a combination of factors is involved.

Each year, more than 18 million Americans -- men and women of all ages, races, and economic levels -- have depression. It occurs more often in women.

Women are especially vulnerable to depression after giving birth. This is a result of the hormonal and physical changes. While new mothers commonly experience temporary "blues," depression that lasts longer than 2-3 weeks is not normal and requires treatment.

Major depression can occur in children and teenagers, and they can also benefit from treatment.

See also: Adolescent depression