Mental illnesses are biological brain diseases which interfere with normal brain chemistry.
Genetic factors may create a predisposition in some people, and life stresses may trigger the onset of symptoms. The most serious of the mental illnesses, schizophrenia is characterized by delusions, hallucinations, impairment in thinking and major changes in behavior and emotions. Two million Americans, one of every 100, have schizophrenia. It can strike at any age, but most often between ages 16 and 25. Schizophrenia is not to be confused with split personality, a rare and very different disorder.