The most prominent symptom of major depression is a severe and persistent low mood, profound sadness, or a sense of despair. The mood change can sometimes appear as irritability. Or the person suffering major depression may not be able to take pleasure in activities that usually are enjoyable.
Major depression is more than just a passing blue mood, a "bad day" or temporary sadness. The mood changes that occur in major depression are defined as lasting at least two weeks but usually they go on much longer — months or even years.
A variety of symptoms usually accompany the mood change, and the symptoms can vary significantly among different people.
Many people with depression also have anxiety. They may worry more than average about their physical health. They may have excessive conflict in their relationships and may function poorly at work. Sexual functioning may be a problem. People with depression are at more risk for abusing alcohol or other substances.
Depression probably involves changes in the areas of the brain that control mood. Nerve cells may be functioning poorly in certain regions of the brain. Communication between nerve cells or nerve circuits can make it harder for a person to regulate mood. These problems may be affected negatively by hormones. An individual's life experience affects these biological processes. And genetic makeup influences how vulnerable any of us is to breakdowns in these functions.
An episode of depression can be triggered by a stressful life event. But in many cases, depression does not appear to be related to a specific event.
Major depression may occur just once in a person's life or may return repeatedly. Some people who have many episodes of major depression also have a background pattern of a milder depressed mood called dysthymia.
Some people who have episodes of major depression also have episodes of relatively high energy or irritability. They may sleep far less than normal, and may dream up grand plans that could never be carried out. The person may develop thinking that is out of step with reality — psychotic symptoms — such as false beliefs (delusions) or false perceptions (hallucinations). The severe form of this is called "mania" or a manic episode. If a person has milder symptoms of mania and does not lose touch with reality, it is called "hypomania" or a hypomanic episode.
If a woman has a major depressive episode within the first two to three months after giving birth to a baby, it is called postpartum depression. Depression that occurs mainly during the winter months is called seasonal affective disorder, or SAD.
Episodes of depression can occur at any age. Depression is diagnosed in women twice as often as in men. People who have a family member with major depression are more likely to develop depression or drinking problems.