The exact causes of anorexia nervosa are unclear, although most specialists believe it is likely to be the result of a combination of factors

Psychological factors

Many people who develop anorexia share certain personality and behavioural traits that may make them more likely to develop the condition. These include:

• a tendency towards depression and anxiety
• finding it hard to handle stress
• excessive worrying and feeling scared or doubtful about the future
• perfectionism – setting strict, demanding goals or standards
• being very emotionally restrained
• having feelings of obsession and compulsion (but not necessarily obsessive compulsive disorder) – unwanted thoughts, images or urges that compel them to perform certain acts

It has also been suggested that some people with anorexia have an overwhelming fear (phobia) of being fat.

Environmental factors

Puberty seems to be an important environmental factor contributing to anorexia. It may be the combination of hormonal changes and feelings of stress, anxiety and low self-esteem during puberty that triggers anorexia.

Western culture and society may also play a part. Girls – and, to a lesser extent, boys – are exposed to a wide range of media messages that constantly reinforce the idea that being thin is beautiful.

Magazines and newspapers also focus on celebrities' minor physical imperfections, such as gaining a few pounds or having cellulite.

Other environmental factors that may contribute towards anorexia include:

• pressures and stress at school, such as exams or bullying, particularly teasing about body weight or shape
• occupations or hobbies where being thin is seen as the ideal, such as dancing or athletics
• a stressful life event, such as losing a job, the breakdown of a relationship or bereavement 
• difficult family relationships
• physical or sexual abuse 

Anorexia often starts off as a form of dieting that gradually gets out of control.

Biological and genetic factors

It has been suggested that changes in brain function or hormone levels may also have a role in anorexia, although it is not clear if these lead to anorexia or if they develop later as a result of malnutrition.

These changes may affect the part of the brain that controls appetite, or they may lead to feelings of anxiety and guilt when eating that improve when meals are missed or after excessive exercise.

The risk of someone developing anorexia is also thought to be greater in people with a family history of eating disorders, depression or substance misuse, which suggests genes could play a role.