Depression is more than just a really bad mood that lasts a long time. It can affect your very identity, it can change who you are. Those who suffer from this all-too-common disorder find that daily life has become too great a challenge. What are the causes of depression? What's behind this disabling disease?

No single cause of depression has been discovered. It seems to result from a combination of factors. These include characteristics that you inherited (genetics), your brain chemistry, conditions in which you grew up and where you live now (environmental factors) and your psychological makeup.

Depression tends to run in families. If depression is a familiar concept from your family life, then you may be more likely to suffer from it yourself. It's unclear whether the more powerful impact is from genetics or learning. Is the tendency to become depressed inherited or is it the way you have learned to cope with events?

Recent research in molecular genetics has discovered a link to the proteins that carry serotonin to neurons in the brain. The chances that traumatic life events will trigger a major depressive episode vary according to which version of the gene 5-HTT you inherited. This seems to indicate that genetics could play a significant role in how prone you are to suffer depression.

Regardless of your personal susceptibility to depression, a depressive episode is almost always triggered by a specific life event. Common triggers of major depression include chronic stress, the death of someone very close to you, or a significant disappointment at home, work or school. Prescription drugs and certain medical conditions can also be at fault. Illnesses often linked with depression include heart attack, stroke, cancer, Parkinsons disease and hormonal disorders. Depression has also been linked to nutritional deficiencies.

Depression is more common in adults over age 65. Although depression should not be considered a normal part of aging, traumatic life events certainly do become more common as we grow older. People retire from lifelong occupations, friends and loved ones die with greater frequency, and advancing years bring increasing health problems. It may surprise you to know that depression occurs at about the same rate in older persons whether they are living in nursing homes or have remained in the community.

No one willingly chooses to suffer from depression. People with depression did not somehow bring the disorder upon themselves with a negative outlook or some personality flaw. Regardless of what caused the major depressive episode that someone may be facing, the important thing is to seek treatment. Treatment is safe and almost always effective. Unfortunately, people in the midst of depression may have difficulty deciding that treatment is needed. That's where friends and family can help.