The exact cause of personality disorders is not known. Many mental health experts believe that early childhood trauma such as physical, sexual or emotional abuse may lead to the eventual development of some personality disorders. For example, patients with borderline personality disorder (BPD) report high rates of childhood sexual abuse. Other stressors that can trigger these conditions include combat, natural disasters, kidnapping, torture and invasive medical procedures.

In addition, studies have shown that some people may be genetically predisposed to developing personality disorders. For example, patients with a family history of schizophrenia are at higher risk of developing schizotypal, schizoid and paranoid personality disorders. Obsessive-compulsive disorder and antisocial personality disorder also appear to have a genetic component.

Other potential risk factors for developing personality disorders include an unstable family life and a childhood head injury.

Avoidant, borderline, dependent and paranoid personality disorders are more likely to occur in women, whereas antisocial personality disorder and obsessive-compulsive disorder are more likely in men.