Depression can affect anyone—even an individual who appears to live a relatively ideal lifestyle.

Researchers believe depression is caused by a combination of several factors including:

• Biochemistry: Differences in certain chemicals in the brain may contribute to symptoms of depression.

• Genetics: Depression can run in families. For example, if one identical twin has depression, the other has a 70 percent chance of having the illness sometime in life.

• Personality: People with low self-esteem, who are easily overwhelmed by stress, or who are generally pessimistic appear to be more likely to experience depression.

• Environmental factors: Continuous exposure to violence, neglect, abuse or poverty may make some people more vulnerable to depression.

Some types of depression tend to run in families, however depression can occur in people without any family history of depression. A personal loss, a difficult relationship, financial problems, and many other stressful situations can contribute to depressive illness.