I read this thing on a website titled "preventing schizophrenia"

Research conducted in the past decade indicates that schizophrenia is due to a genetic predisposition and environmental stressors early in a child's development (during pregnancy and birth, and/or early childhood) which lead to subtle alterations in the brain that make a person susceptible to developing schizophrenia. Additional environmental factors and stresses later in life (during childhood, adolescence and young adulthood) can either damage the already vulnerable brain further and trigger schizophrenia or lessen the expression of neurodevelopmental defects and decrease the risk of schizophrenia. In fact experts now say that schizophrenia (and all other mental illness) is caused by a combination of biological, psychological and social factors, and this understanding of mental illness is called the bio-psycho-social model.