Though the cause of personality disorders isn't known, both genetics and environment are suspected to play a part in its development. Some mental health professionals speculate that a bleak childhood where warmth and emotion were absent contributes to the development of the disorder. A higher risk for schizoid personality disorder in families of schizophrenics suggests that there is genetic susceptibility to developing this disorder.
Those with schizoid personality disorder do not have schizophrenia, but it is thought that many of the same risk factors in schizophrenia may cause schizoid personality disorder.