Psychosis, << sy KOH sihs, >> is a term used to describe a severe mental illness. Psychoses (the plural of psychosis) are characterized by a variety of symptoms that most people consider abnormal. These include hallucinations, such as hearing voices when no one is around, and delusions, such as the notion that one is being persecuted or conspired against (see Hallucination ; Delusion ).
Some psychoses have obvious physical causes. For example,a brain tumor may cause hallucinations. Or, an infection may affect the brain, as in delirium due to pneumonia. These are called organic psychoses. In toxic psychoses, a harmful chemical, or toxin, affects the brain. Examples include psychosis caused by lead poisoning or certain drugs. Other psychoses have no obvious physical cause. The most common psychotic disorder is schizophrenia (see Schizophrenia ).
