Schizophrenia is part of the group of a mental illness that falls into the category of psychotic disorders. Schizophrenia is in the majority of cases a chronic lifelong mental illness characterised by repeated relapses and remissions. It is associated with repeated episodes of psychosis, apathy and social withdrawal, and cognitive impairment. This has can have an impact in a wide area of functioning including work, school, parenting, self-care, independent living, interpersonal relationships and leisure pursuits. It is one of the world's top ten causes of long-term disability and affects about 1% of the world's population. That is a staggering amount of people if you consider that the world's population is just over 7 billion currently.
The actual answer to "what is schizophrenia?" is still being researched. Researches have not found the cause of schizophrenia. Although schizophrenia is discussed as a single disorder, it probaby comprises a group of disorders with various causes, and includes patients whose clinical presentations, treatment response and course of illness varies. Schizophrenia is a syndrome (pattern) of symptoms at present which represents changes in function (dysfunction) across a number of domains in the brain. These domains are those of perception, mood, volition, motor skills, language, higher executive functioning, and memory. These symptom complexes are discussed further under positive, negative and cognitive symptoms. One modern viewpoint is that all the major mental illness are caused by varying degrees of dysfunction across these domains, and that they are not discrete separate diseases. For instance, bipolar disorder would have more significant mood disturbance and less perceptual disturbance, and schizophrenia woudl be at the opposite end of the spectrum with more perceptual disturbance than mood disturbance.
Clinically schizophrenia is diagnosed according to certain criteria. See the diagnostic criteria from the DSM IV Text Revised version. In summary symptoms should be present for at least one month and there must be a functional change in the person of at least 6 months duration. The latest version V is due in the next few years but no major changes are expected to the diagnostic criteria for Schizophrenia.
So to know what is schizophrenia, one has to understand what is psychosis or a psychotic symptom. It actually refers to the same thing. Firstly there are 2 types of psychotic symptoms, viz positive and negative.
These are not termed "positive symtoms" because they are "positive" or "good" in any way. They get this name because they are an addition to what the patient usually experiences. So these include the additional voices, images and thoughts which patients experience. Click on Positive Symptoms to get a further description of these.
The "negative symptoms" are termed such because there is a loss of certain aspects of the person. There can be a loss of emotional connection, there can be a loss of facial emotional expression, and there may be a loss of motivation and initiative, and social withdrawal. The negative symptoms can also describe someone who sits and says nothing the whole day or who is unable to engage in any conversation due to being empoverished in their thinking.