LOS ANGELES, CA - JULY 24: Actress Olivia Munn arrives at a screening of Millennium Entertainment's 'The Babymakers' at the Silent Movie Theatre on July 24, 2012 in Los Angeles, California. (Photo by Kevin Winter/Getty Images)

Actress Olivia Munn recently revealed that she pulls out her eyelashes as a result of the "impulsive control" disorder trichotillomania. People with the disorder have the urge to pull out their hair, whether it be on their scalp, eyelashes, eyebrows or elsewhere on the body, leading to thinned hair.

"I don't bite my nails, but I rip my eyelashes," Munn, 32, told the New York Daily News. "It doesn't hurt, but it's really annoying. Every time I run out of the house, I have to stop and pick up a whole set of fake eyelashes."

As many as 4 percent of people may have trichotillomania, according to the National Institutes of Health, and the condition is four times more common among women. The disorder is usually first seen before people reach age 17, and the period of hair-pulling usually only lasts for about a year, the NIH said.

Symptoms of trichotillomania include actually pulling your hair out; wanting to pull the hair out and feeling relieved after you've pulled it out; playing, chewing, eating or rubbing the extracted hair; and having patchy, bald or sparse areas on the body where the hair used to be, according to the Mayo Clinic.

"They may spend hours in front of a mirror in these very odd postures trying to locate that one hair that they know is there that they feel doesn't belong," trichotillomania expert Dr. Nancy Keuthen told ABC News.

People may also feel tense either right before, or if trying to resist, pulling out the hair, according to Mental Health America.

"Whenever I get emotional, or sometimes very stressed, or if I'm upset, I go for my hair," Jena Metts, who at the time had trichotillomania, told ABC News in 2008. "And [it's] perfectionism sometimes. If there's like a little hair sticking out, I want to pull it."

The exact cause of the condition isn't known, but the Mayo Clinic reports that it may be a result of genetics and the environment, and possibly even differences in brain chemicals.

Not all doctors agree on the treatment method for trichotillomania, according to the National Institutes of Health. Some may prescribe medicines like selective serotonin reuptake inhibitors or naltrexone; for other cases, habit reversal techniques or behavioral therapy can help to stop the hair-pulling.

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