This is a great question! There isn’t a straightforward answer to the question ‘What causes depression?’, because there are lots of different things that can make people develop depression.
Some people’s depression is triggered by one or more of these things. Other people might experience the same things without developing depression. And some people might develop depression without being able to identify an obvious reason or cause.
It’s probably not a chemical imbalance
The evidence suggests that it isn’t a chemical imbalance that causes depression.
It’s true that antidepressants work by changing brain chemistry and that they help some people with depression to feel better. But this doesn’t necessarily mean that the medication is ‘fixing’ something that was ‘wrong’ with their brain chemistry. It might help in a different way – like how painkillers can help a headache, even though a headache isn’t caused by a lack of painkiller!
If there are changes to the brain chemistry of depressed people, we’re not sure whether they cause depression or whether they happen as a result of depression.
Our brains are really complicated – so it’s OK if you find it helpful to think about antidepressants helping your brain chemistry.
Going through difficult experiences when you’re a child or young person can affect how you think about yourself and how you manage your feelings. Because of this, it might be harder for you to cope with things, and you might be more at risk of developing depression.
Lots of people think of ‘difficult experiences’ as big, traumatic events. But going through lots of small, difficult experiences can have a bigger impact on someone than one traumatic event.
Almost everyone will experience some things that are stressful or upsetting (like a relationship ending or someone they love dying) at some point. Some people experience traumatic events like being assaulted or being bullied or abused.
After something difficult has happened, it’s normal to need some time before you feel OK again. But some people become depressed after a difficult event, especially if they don’t have much support (for example, friends or family to talk to).
We know that people who have a close family member with depression are more likely to experience depression themselves.
We don’t know whether this is because of biology (for example, the genes you inherit from your parents) or because lots of people learn behaviours and ways of coping from their family members.
Other mental health problems
It’s common for people with other mental health problems (like anxiety, eating problems, or PTSD) to experience depression. Coping with the symptoms of another mental health problem can be really tough – and for some people this might trigger depression.
Illness, disability, or physical health problems
Disabled people can find themselves excluded from things because of inaccessibility. It can also be difficult for people with physical health problems to live with and manage their symptoms. This can have a big impact on their mood.
There are also some physical health problems that can cause depression, including hormonal problems, symptoms related to the menstrual cycle (the process that causes periods), low blood sugar, and sleep problems.
Finally, head injuries can cause depression and other emotional problems.
Alcohol and drugs (including medication)
Medication for other conditions (for example, allergies and birth control) can affect people’s mental health and cause depression. Doctors can often help people find alternative medications if they think a medicine that they’re taking is causing them to be depressed.
We also know that alcohol and drugs can cause depression. Some people might begin to use them because they want to feel better or distracted – but in the end they may end up feeling worse overall.
Social and economic circumstances
Some evidence suggests that depression is more common in people who live in difficult social and economic circumstances. This includes things like whether they live in poverty, whether they have a safe place to live, and whether they have supportive people in their lives.
When things all add up
A lot of people with depression find that there might be more than one reason for their depression.
Sometimes it might be that people are already at-risk of developing depression because of factors like their family background or childhood experiences, they then develop depression after a difficult life event or illness.
Other people might experience a few difficult life events in a row, or experience something difficult, withdraw from family and friends, and start using alcohol or drugs to cope.