What are the most common causes of paranoia?

Psychiatric paranoia includes paranoid personality disorder, paranoid schizophrenia and delusional (paranoid) disorder. The identifying mark of paranoid personality is fear and expectation of attack and betrayal. Paranoid personalities are suspicious, touchy, quick to take offense and slow to forgive, self-righteous, and often argumentative. Paranoid personalities find causal connections everywhere; nothing is coincidental. They think that others are taking special notice of them and see references to themselves in innocuous behavior and irrelevant events. They are constantly on guard, searching for hidden motives and meetings.