While the exact cause of depression isn't known, a number of things can be associated with its development. Generally, depression does not result from a single event, but from a combination of recent events and other longer-term or personal factors.
Research suggests that continuing difficulties – long-term unemployment, living in an abusive or uncaring relationship, long-term isolation or loneliness, prolonged exposure to stress at work – are more likely to cause depression than recent life stresses. However, recent events (such as losing a job) or a combination of events can ‘trigger' depression in people who are already at risk because of past bad experiences or personal factors.
- Family history – Depression can run in families and some people will be at an increased genetic risk. However, this doesn't mean that a person will automatically experience depression if a parent or close relative has had the illness. Life circumstances and other personal factors are still likely to have an important influence.
- Personality – Some people may be more at risk of depression because of their personality, particularly if they have a tendency to worry a lot, have low self-esteem, are perfectionists, are sensitive to personal criticism, or are self-critical and negative.
- Serious medical illness – Having a medical illness can trigger depression in two ways. Serious illnesses can bring about depression directly, or can contribute to depression through associated stress and worry, especially if it involves long-term management of the illness and/or chronic pain.
- Drug and alcohol use – Drug and alcohol use can both lead to and result from depression. Many people with depression also have drug and alcohol problems. Over 500,000 Australians will experience depression and a substance use disorder at the same time, at some point in their lives.
Changes in the brain
What happens in the brain to cause depression is not fully understood. Evidence suggests it may be related to changes in the levels or activity of certain chemicals – particularly serotonin, norepinephrine and dopamine – which are the three main chemicals related to mood and motivation that carry messages within the brain. Changes to stress hormone levels have also been found in people with depression. Research suggests that behaviour can affect brain chemistry – for example, long-term stress may cause changes in the brain that can lead to depression. Changes in brain chemistry have been more commonly associated with severe depression rather than mild or moderate depression.
Everyone is different and it's often a combination of factors that can contribute to a person developing depression. It's important to note that you can't always identify the cause of depression or change difficult circumstances. The most important thing is to recognise the signs and symptoms