Being careful and guarded is one thing, but when paranoia becomes pervasive and problematic, it's something very different. "People who have a more suspicious personality style are likely aware on some level that they are more guarded than others," Greenberg says. "People who are paranoid and psychotic have much more trouble being aware of the fact that they see things differently than others. The classic example is someone who really believes they are being followed by the FBI. There is no convincing them that this is not the case. To be clear, though it's easy to minimize the distress of people in these situations, they are often very distressed and anxious and endure a great deal of suffering. Paranoia of this kind can occur in schizophrenia and in delusional disorders. Paranoid delusions can also occur in some neurological disorders such as in some dementias. Sadly, paranoid delusions can severely disrupt life and functioning."
Paranoid personality disorder (PPD) is one example of intense paranoia that is no longer just a personality quirk but something serious. Paranoia is the essential characteristic that people with PPD all have in common, but the beliefs they hold aren't just run-of-the-mill cautionary ways of thinking. People with PPD often have unfounded beliefs and tend to blame and distrust others in ways that "interfere with their ability to form close or even workable relationships." The disorder usually begins in childhood or early adolescence and seems to be more common in men than in women. According to the Cleveland Clinic, PPD affects between 2.3 percent and 4.4 percent of the general population.
Unfortunately, clinical paranoia is tough to diagnose until the symptoms progress from mild to severe and because PPD often co-occurs with another mental health problem, like an anxiety disorder, obsessive-compulsive disorder (OCD), and depression, it can often be mistaken for something else.
Treatment can be challenging as well. "If someone is paranoid and severely mentally ill, it can be hard to get help, as the person will tend not to trust doctors, worry that medication may be harmful and they may come across as angry toward others," Greenberg says. "They may not even feel angry, but when someone is really paranoid, there are so many things in the environment they have to keep track of and this makes interactions with others difficult. For example, it's hard to have a conversation if you are wondering what someone might try to do to you, if you are being watched or followed or even what a slight change of expression on someone else's face might mean."