What is the major cause of mental illness?

The causes of the mental illnesses remain a mystery. However they are associated to a combination of biological, psychological and environmental factors.

Biology is involved because some disease are caused because of a chemical imbalance in the body. For example, researchers have discovered that schizophrenia is related to a failure in specific neurotransmitters* of the brain, like dopamine. Also, some disease might also be related to brain structure. Some people who suffers from some diseases can have a different brain structure to others
that don´t have the illness. Mental illness is also related to heredity, if a member of a family has suffered from a mental illness, then people in that family may have a major risk to suffer it too.

Mental illness can also be the result of stress or trauma. For example, a PTSD can occur after a big, horrible event in someone's life or a Major Depression can appear after a trauma and a period of intense stress.

Social pressure can also be a cause of mental illness. For example, eating disorder, such as anorexia or bulimia, may appear. mostly among teenagers, because of the constant pressure they experience
 given the standards, sometimes unattainable, that society marks.

*neurotransmitter: substances the brain cells use to communicate with each others.