Millions of Americans may be struggling to cope with people who have personality disorders, a form mental illness in which people have trouble functioning with others, according to an expert.

A recent government survey estimated that nearly 15 percent of Americans have a personality disorder.

Consequently, Dr. Stuart C. Yudofsky of Baylor College of Medicine in Houston, Texas estimated that another 15 to 30 percent of people have a close relationship with someone - perhaps a co-worker, partner or family member - who has antisocial personality disorder, borderline personality disorder, or some other personality disorder.

People with the histrionic type of personality disorder, a common condition, are impulsive and quickly form intense but shallow relationships. People with borderline personality disorder are typically unstable, exhibit wild mood swings, and have self-destructive behavior. Other personality disorders include narcissistic, paranoid, schizotypal, and addictive types.

Yudofsky discusses how to recognize and shield yourself from the effects of people with personality disorders in a new book called “Fatal Flaws: Navigating Destructive Relationships With People With Disorders of Personality and Character.”

Yudofsky told AMN Health that he calls personality disorders “fatal flaws” because in many cases, people with the disorders won’t accept that they have a problem, or seek treatment for it. However, people with personality disorders who are open to treatment have an “excellent” chance of recovery, he added.

To help people recognize personality disorders in their relationships, Yudofsky has assembled a series of questions - for instance: Do you trust the person in question? Do you feel like your needs are as important as his or hers? “And if you get a certain number of noes, it should raise your index of suspicion,” he said.

To protect ourselves from others with personality disorders, who are often extremely successful and charming, it’s important to set “safe, ethical boundaries,” Yudofsky said in an interview.

For instance, someone with an antisocial personality disorder - often associated with violent or deviant behavior - may ask you to bring him or her supplies from your office, he said. Rather than jeopardize your company’s trust, it’s better to just refuse, Yudofsky recommended.

And if a person with a personality disorder keeps telling you that you’re not skilled at something, set boundaries between what he or she thinks of you and what you think of yourself, so that the words don’t affect your self-confidence, he added. “You make your own decisions about what kind of person you are,” he said.

Once you’ve recognized a personality disorder in someone you know, you ultimately need to decide if the benefits of being around him or her outweigh the risks, Yudofsky noted. That is a difficult decision, and to make it, many people may need the advice of an impartial observer, such as a mental health professional, Yudofsky added.