There is no single cause of depression, and people develop depression for different reasons.
Depression has many different triggers. For example, upsetting or stressful life events, such as loss of a loved one, divorce, illness, redundancy and job or money worries, can be the cause.
It is not uncommon to find that different causes combine to trigger depression, such as you may feel low after an illness and then experience a stressful life event, such as bereavement, which leads to depression.
People often talk about a 'downward spiral' of events that leads to depression.
Depression is complex and a number of things can increase the risk of developing it.
Stressful life events
Stressful life events such as divorce when for example you stop seeing friends, withdraw from social events, maybe drink more at home. All of this can make them feel even worse and trigger depression.
Those people who suffer with a chronic disease such as Fibromyalgia of rheumatoid arthritis, or life-threatening illness such as cancer are at higher risk of developing depression. Head injuries are also an often under-recognised cause of depression causing changes in mood and emotional problems.
You may have inherited certain genes from your parents giving you certain personality traits, or early life experiences affecting the way you think. These can have a marked effect on the way you think in later life.
Family history of depression
Research shows that some genes increase the risk of depression after a stressful life event.
Some women are particularly vulnerable to depression after pregnancy. The hormonal and physical changes, as well as the added responsibility of a new life, can lead post natal depression.
Becoming cut off from family and friends may increase your risk of depression, or it may be a response to feeling depressed as the downward spiral takes hold.
Alcohol and drugs
Use of these substances in the long term can result in feelings of depression.
Diagnosis of depression
See your GP if you think you have depression. Unfortunately, there's no brain scan or blood test that can be used to diagnose when a person has a depressive illness. The diagnosis can only be made from the symptoms.
Generally speaking a diagnosis of depression will be made if a person has a persistently low mood that significantly influences their everyday life and has been present for two weeks or more, and there are also three or four or more other symptoms of depression.