Schizophrenia is a treatable brain disorder that has affected people throughout history. About 1% of the population develops it during their lifetime. Schizophrenia appears to have a genetic link, but there are many factors that may cause or increase the risk of developing it, including psychological, environmental and social factors . Current research suggests that schizophrenia is caused by a chemical imbalance in the brain and may be related to excessive dopamine activity.

There are five subtypes of schizophrenia: catatonic, disorganized, paranoid, residual and undifferentiated. The type of disorder someone has will determine the types of symptoms they experience (e.g., hallucinations, delusions) and how severely affected they are by the illness (i.e., level of functioning).

Catatonic Type: Involves abnormal movements, such as a lack of response or a delay in response to stimuli, and/or excessive and purposeless movement. This subtype also involves extreme negativism (resistance to instructions or attempts by others to be moved) or mutism . Catatonia is often associated with schizophrenia and can sometimes be an early warning sign of the disorder.

Disorganized Type: This subtype involves disorganized thinking (e.g., having trouble organizing thoughts or speaking coherently), flat or inappropriate emotions (e.g., showing little reaction to very sad or disturbing circumstances) and odd behavior (e.g., wearing several layers of clothing even when it’s hot).

Paranoid Type: This subtype involves delusions and auditory hallucinations that frequently involve the person holding strong beliefs that others are trying to harm them or their property (e.g., believing that people on television or radio are sending special messages just for them, thinking strangers are talking about them when the conversation is in fact about something else).

Residual Type: This subtype involves having some, but not all of the symptoms required for a diagnosis of schizophrenia. It mostly affects cognitive function (e.g., difficulties with memory, attention and concentration) rather than emotional problems associated with psychosis.

Undifferentiated Type: This subtype is diagnosed when a person has symptoms that meet the general diagnostic criteria for schizophrenia, but not those for any one of the other subtypes.

In addition to these five subtypes, two other classifications are sometimes used: Disorganized/Hebephrenic and Paranoid. Symptoms of the disorganized/Hebephrenic subtype are very similar to the disorganized subtype, but are not as severe. The paranoid subtype involves delusions and hallucinations only (i.e., no significant problems with other thought or behavior patterns).