There is no single cause of depression, you can develop it for different reasons.
Depression has many different triggers. For some, an upsetting or stressful life event, such as bereavement, divorce, illness, redundancy and job or money worries, can be the cause.
Often, different causes combine to trigger depression. For example, you may feel low after an illness and then experience a traumatic event, such as bereavement, which brings on depression.
People often talk about a 'downward spiral' of events that leads to depression. For example, if your relationship with your partner breaks down, you're likely to feel low, so you stop seeing friends and family, and you may start drinking more. All of this can make you feel even worse and trigger depression.
Some studies have also suggested you're more likely to get depression as you get older and that it's more common if you live in difficult social and economic circumstances.
Stressful events
Most people take time to come to terms with stressful events, such as bereavement or a relationship breakdown. When these stressful events happen, you have a higher risk of becoming depressed if you stop seeing your friends and family and you try to deal with your problems on your own.
Illness
You may have a higher risk of depression if you have a long standing or life-threatening illness, such as coronary heart disease or cancer.
Head injuries are also an often under-recognised cause of depression. A severe head injury can trigger mood swings and emotional problems.
Even a minor head injury can damage the pituitary gland, which is a pea-sized gland at the base of your brain that produces thyroid-stimulating hormones. This can cause a number of symptoms, such as extreme tiredness and a loss of interest in sex, which can in turn lead to depression.
Personality
You may be more vulnerable to depression if you have certain personality traits, such as low self-esteem or being overly self-critical. This may be due to the genes you've inherited from your parents, or because of your personality or early life experiences.
Family history
If someone else in your family, such as a parent or sister or brother, has suffered from depression in the past, then it's more likely that you will too.
Giving birth
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 to postnatal depression.
Loneliness
Becoming cut off from your family and friends can increase your risk of depression.
Alcohol and drugs
Some people try to cope when life is getting them down by drinking too much alcohol or taking drugs. This can result in a spiral of depression.
Cannabis helps you relax, but there is evidence that, especially in teenagers, it can bring on depression.
And don't be tempted to drown your sorrows with a drink. Alcohol actually makes depression worse.
