Feeling down or sad once in a while is normal. However, when these feelings overtake your day-to-day life and impair your ability to work, eat, sleep and play, depression may be the culprit. There is no one single factor that can cause severe depression; it is the result of a culmination of biological, chemical and environmental factors. Whatever the specific causes of depression, the National Alliance on Mental Illness (NAMI) notes that scientific research has established that severe depression is a medical illness and should be treated as such.
Chemical Imbalance
There are three neurotransmitters that act as messengers transmitting electrical signals to and from brain cells. They are chemicals known as norepinephrine, serotonin and dopamine. According to HelpGuide.org, it is believed by many in the scientific community that when a chemical imbalance occurs in these neurotransmitters, depression can occur. Antidepressant medications target the levels of these chemicals to return them to normal and minimize the symptoms of depression.
Family History
Scientific evidence points to a genetic predisposition to major depression, according to the NAMI website. While not all people with a family history will develop depression, it is likely that these people are more vulnerable to it. The Mental Health Channel website reports that a person has a 27 percent chance of inheriting a mood disorder from one parent, and this chance doubles if both parents are affected.
Life Events
Whether physical or emotional, life events can trigger a severe episode of depression. Examples of such traumatic life events include the death of a loved one or a major loss or change, such as what might happen with a job loss or even a move. Heart disease or cancer are severe or long-term illnesses that can lead to an episode of depression. According to the Mental Health Channel website, depression is more common in people with a history of sexual or physical abuse and in areas afflicted with war, natural disasters, poverty or neglect.
