Psychosis may be caused by the interaction of biological and psychosocial factors depending on the disorder in which it presents; psychosis can also be caused by purely social factors, with no biological component.

Biological factors that are regarded as contributing to the development of psychosis include genetic abnormalities and substance use. With regard to chromosomal abnormalities, studies indicate that 30% of patients diagnosed with a psychotic disorder have a microdeletion at chromosome 22q11. Another group of researchers has identified the gene G72/G30 at chromosome 13q33.2 as a susceptibility gene for childhood-onset schizophrenia and psychosis not otherwise specified.

With regard to substance abuse, several different research groups reported in 2004 that cannabis (marijuana) use is a risk factor for the onset of psychosis.

Migration is a social factor that influences people's susceptibility to psychotic disorders. Psychiatrists in Europe have noted the increasing rate of schizophrenia and other psychotic disorders among immigrants to almost all Western European countries. Black immigrants from Africa or the Caribbean appear to be especially vulnerable. The stresses involved in migration include family breakup, the need to adjust to living in large urban areas, and social inequalities in the new country.