Depression may be described as feeling sad, blue, unhappy, miserable, or down in the dumps. Most of us feel this way at one time or another for short periods.

True clinical depression is a mood disorder in which feelings of sadness, loss, anger, or frustration interfere with everyday life for weeks or longer.

The exact cause of depression is not known. Many researchers believe it is caused by chemical changes in the brain. This may be due to a problem with your genes, or triggered by certain stressful events. More than likely, it's a combination of both. Some types of depression run in families. But depression can also occur if you have no family history of the illness. Anyone can develop depression, even kids.

The following may play a role in depression: alcohol or drug abuse, certain medical conditions, including underactive thyroid, cancer, or long-term pain. Using certain medications such as steroids, sleeping problems, stressful life events, such as: breaking up with a boyfriend or girlfriend, failing a class, death or illness of someone close to you, divorce, childhood abuse or neglect, job loss, social isolation (common in the elderly).