As with all mental health conditions, depression is not caused by just one single factor. Depression has many possible causes, including faulty mood regulation by the brain, genetic vulnerability, stressful life events, medications, and medical problems. It's believed that several of these forces interact to bring on depression.
The complexity of the disorder also means that two people may have similar symptoms of depression but what causes the depression may differ for both.

There have been several main causes of depression which have been identified.

  1. Negative life events
  2. Thinking styles
  3. Biology
  4. Genetics
  5. Medication and other health problems

Negative Life Events

Depressed mood may be triggered by stressful life situations.

Examples of negative life situations are:

  • Stress directly related to the workplace such as job insecurity, unpleasant work area, overworked.
  • Major life events such as death of a loved one, divorce or job loss.
  • Lack of contact with other people or ongoing relationship conflict.
  • Stress related to physical health especially health problems that are chronic or cause a lot of pain.

If your attempts to cope with these situations have not been successful – or the situations have not improved – you may begin to feel overwhelmed and hopeless. Risk of developing depression may then increase.

Thinking Styles

Research has found that certain patterns of self-statements and thoughts makes people vulnerable to depression. Often these thinking styles are automatic and out of awareness. These are known as cognitive distortions.

Common examples of these thinking styles are:

  1. Black & White thinking: People have this type of thinking when they can only see one extreme or the other. We are right or wrong, good or bad. There is no middle ground with shades of gray. If your performance falls short of perfection, it means you are a complete failure.
  2. Over-generalization: People overgeneralize when they come to a general conclusion based on a single incident or a single piece of evidence. For instance, if you failed an exam, you may expect that you will fail every exam after that.
  3. Catastrophizing: People expect a bad outcome no matter what.  For example, a person might exaggerate the importance of small events (such as their mistake, or someone else’s achievement). A relatively small event feels overwhelmingly awful, bad and terrible.
  4. Personalisation. People personalise when the person believes that everything others do or say is about the person. A person engaging in personalization may also see themselves as the cause of some negative external event that they were not responsible for.
  5. Mental filtering. This happens when people focus exclusively on negative aspects of a situation and ignores any positive outcome. For instance, you were out for dinner with your best friends. Everyone was having a great time including you until your friend said something about your shirt being old-fashioned. That ruined the night and you could only focus on your friend's comment.This could also happen with the way you remember things. It is sometimes easier to remember the negative events and harder to remember the positive things, particularly when someone is depressed.
  6. Jumping to conclusions. We jump to conclusions when we arrive at conclusion without much evidence to support it. This happens when we mind-read by making assumptions about what someone else is thinking or why people do what they do. People who mind-read negative interpretations tend to be at risk for depression. Sometimes these conclusions are reflections of how we think about ourselves and reflect our insecurities, rather than the reality of what others do think.We can also jump to conclusion when we make predictions about what is going to happen in the future. We believe that bad things will happen, despite not much evidence that these bad events will actually occur. Anticipating negative events is also strongly associated with anxiety and stress.
  7. Labelling. This happens when we make global statements about ourselves or others, based on behaviours in specific situations. For instance, if you fail an exam, a label would be "bad student" or "lazy". But this could be the only exam you failed out of hundreds that you have taken. This label is an inaccurate description of the true situation but leads you to feel bad anyway.


Our understanding of the neurological underpinnings of mood is incomplete. Thus far, nerve cell connections, nerve cell growth, and the functioning of nerve circuits have been implicated in depression.

1. Brain region.

Brain regions regulate mood and how other functions, such as memory, may be affected by depression. Areas that play a significant role in depression are the amygdala, the thalamus, and the hippocampus.

The amygdala is part of the limbic system, a group of structures deep in the brain that's associated with emotions such as anger, pleasure, sorrow, fear, and sexual arousal.

The thalamus receives most sensory information, relays it to the appropriate part of the cerebral cortex and helps link sensory input to pleasant and unpleasant feelings.

The hippocampus is part of the limbic system and has a central role in processing long-term memory and recollection. The hippocampus is smaller in some depressed people, and research suggests that ongoing exposure to stress hormone impairs the growth of nerve cells in this part of the brain.

2. Neurotransmitters.

Neurotransmitters are chemicals that relay messages from neuron to neuron. Examples of neurotransmitters which have been implicated in depression are:

Serotonin helps regulate sleep, appetite, and mood and inhibits pain. Research supports the idea that some depressed people have reduced serotonin transmission. Low levels of a serotonin byproduct have been linked to a higher risk for suicide.

Norepinephrine constricts blood vessels, raising blood pressure. It may trigger anxiety and be involved in some types of depression. It also seems to help determine motivation and reward.

Dopamine is essential to movement. It also influences motivation and plays a role in how a person perceives reality. Problems in dopamine transmission have been associated with psychosis, a severe form of distorted thinking characterised by hallucinations or delusions. It's also involved in the brain's reward system, so it is thought to play a role in substance abuse.

Brain cells usually produce levels of neurotransmitters that keep senses, learning, movements, and moods perking along. But in some people who are severely depressed or manic, the complex systems that accomplish this go awry. For example, receptors may be oversensitive or insensitive to a specific neurotransmitter, causing their response to its release to be excessive or inadequate.


A person who has a first-degree relative who suffered major depression has an increase in risk for the condition of 1.5% to 3% over someone who does not have a first-degree relative who has experienced major depression.

Genes could affect people's reaction to stress. For instance, researchers found that people with a particular variant in a serotonin transporter gene (5-HTT) were more likely to become depressed in response to stress.

Medication and other Health Problems

Symptoms of depression or mania could be a side effect of certain drugs, such as steroids or blood pressure medication. Be sure to tell your doctor or therapist what medications you take and when your symptoms began.

Certain medical problems are linked to lasting, significant mood disturbances. For instance, two common physical conditions associated with mood disturbances are two thyroid hormone imbalance. An excess of thyroid hormone (hyperthyroidism) can trigger manic symptoms. On the other hand, hypothyroidism, a condition in which your body produces too little thyroid hormone, often leads to exhaustion and depression.