What causes mental illness?

Just like any other illness, such as cancer or diabetes, mental illnesses have their own specific names and effects. It’s a complicated area which doctors and scientists are still researching.

Mental illness usually happens as a result of a combination of different things, rather than just one single cause. The factors that are known to play a role in mental illness are:

  • Genetics: the unique mixture of genes you inherit from your parents
  • Epigenetics: transgenerational influences
  • Early environment: pre and post birth circumstances and stressors
  • Current environment: the personal situation of the person, including all the elements such as family circumstances, social life, siblings, parents, teachers etc.
  • Family pattern: the unique ways of managing that every family develops

It is a combination of these five things that influence someone getting a mental illness. These five things can be grouped into two different categories.

  • Biological factors (genes and epigenetics): These are the codes in each of our cells which ‘suggest’ how we should develop. We are born with these.
  • Environmental factors (early environment, current environment, family pattern): This is what’s going on around us, both from when we were growing up and in the present day.

Biological factors


In case you have not heard of these, they are little bits of the chromosomes, which are long threads in each cell of our body which carry all the information – like computer programmes – which tell our bodies how to develop.


This is still a science that is relatively new, but it seems that what we do in our lives can sometimes effect our children or grandchildren. This type of information is not exactly carried in your genes, but in other parts of our cells.

We say that the genetics and epigenetics ‘suggest’ how our bodies should develop because they do not generally actually decide how we develop. This is because their effect can be changed so much by the environment we grow up in. Apart from one or two very rare special illnesses, genes do not decide if we become mentally ill or not. See ‘Will I catch or inherit my parent’s mental illness’ for more information.

Supposing you are a person who is very nervous about being with people, if you can develop say one friendship and then that leads to two or three more friends you can trust, you can gradually learn to be less afraid of people and less shy.


Early Environment

Events that happen in childhood may contribute to someone having problems later in life.

Current Environment

Social factors: Poverty, lack of social support, discrimination and unemployment are very important factors which play a part in everyone’s mental health. Regardless of how well someone is coping, if some of these factors are present, they are likely to play a role in how well an individual can deal with situations.

Life events: Major life events like ill-health, bereavement, unemployment, breakup of a relationship or divorce, moving house or leaving home for the first time can put pressure on someone’s ability to cope. Even positive, desired or chosen events, such as marriage or childbirth, can have the same effect. They may also increase a person’s vulnerability to becoming unwell.

Medical conditions: Certain physical conditions such as thyroid dysfunction or anaemia can sometimes play a role in depression. Your doctor may have tests to see if these conditions are present.

Because of the individual nature of mental illness, it is important to remember it is not the thing that happens in life itself, but the way the person sees that life event, that may play a part in them developing a mental health problem.

Family Patterns

People learn ways of behaving and thinking, which may help or hinder them when coping with situations they face later in life. What they learn depends on the experiences they have in childhood, as well as the people they have around them to learn from. For example, when a crisis happens some people may see others panicking, so pick up that way of responding whenever something challenging happens.

All five factors

We’re talking about all these factors having an influence when someone develops a mental illness. These biological and environmental factors can also affect your personality type and coping strategy. You can see this in your different friends; people vary in character and react to the same situation in very different ways. The factors that influence your vulnerability to developing a mental illness are the same factors that influence your personality and how you cope with life. People have different temperaments; some people are more sensitive or outgoing, or more talkative or shy. And your personality and temperament also shape your coping style, the typical way that you respond to situations and events.

Everyone is unique, they have unique genes and have lived in an environment that is unique to them. You may be able to think of families you know where different children have very different personalities, even though they grow up in the same household with the same parents. Therefore, what causes a mental illness in individuals is unique to them and cannot be down to just one thing.

Are mental illnesses caused by a chemical imbalance?

You will probably have heard someone say that mental illness is caused by an imbalance of chemicals in the brain. This may sound like a simple idea – as though there are too much or too many chemicals or not enough – but the real reason is more complicated.

The first thing to realise, is that chemicals make up everything: water, salt, sugar, in fact, everything in our bodies, everything we eat and everything we see and touch or smell. In all animals – including us humans – chemicals only work when they are organised to do a particular job in a particular way/in a particular place. So the chemicals are not just floating about in the brain like a kind of soup. They are simply part of the complicated structures which make up our brains, and help to make it work so that it controls our body, as well as what we think and feel.

Developing a mental illness

Given a certain kind of stress in a specific amount, all of us can develop mental illness. However, the type of stress will vary from individual to individual, just as some people may have a vulnerability to one kind of illness rather than another. Also, when you experience this stress, it can affect you in different ways. If you experience stress in your childhood it can affect how you develop and therefore become part of your mental processes.

So how a person can manage stress will also be influenced by their earlier experiences of stress, which will affect their resilience (their ability to bounce back to a happy balanced life). Some people may be more vulnerable to developing mental illness, but in general, life events and stress play a major part in this vulnerability being triggered.

So… in a nutshell

Mental illness is a result of several factors, which include the person’s inherited characteristics and life experiences. While mental illness is not anyone’s fault, learning about yourself and the factors which affect you can help to significantly protect you from mental illness.

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