WEDNESDAY, Nov. 19 (HealthDay News) -- Did you just get shot down by a co-worker who has no interest in going on a date? Look at the bright side: New research suggests that rejection may boost your ability to detect insincere smiles.

People who were thinking about being rejected recognized 80 percent of fake human smiles shown on a computer monitor, the study found. By comparison, other study participants were only able to detect insincere smiles about half of the time.

It's not clear why rejection may boost the ability to figure out when someone else is faking an emotion. It may have something to do with a primitive need to fit in with others and to detect what they're really thinking, said study lead author Michael Bernstein, a graduate student at Miami University in Ohio.

"People who are rejected have got to be really concerned about getting back into a group," he said.

Humans can easily fake smiles when they aren't feeling any positive emotions. Detecting an insincere smile isn't easy, however, although there are clues if you look closely, Bernstein said.

"A real smile is an automatic process. It involves muscles that are not involved when you make a fake smile," he said. "All smiles involve muscles around the mouth, but only real smiles involve muscles around the eye."

A real smile indicates signs that someone wants to work with another person and cooperate, Bernstein said. "With a fake smile, you might be feeling good and wanting to cooperate, but you might be hiding something."

Mark Frank, director of the Communication Science Center at the University of Buffalo, thinks people may not want to fully understand other people's motivations as expressed through their facial expressions.

"This is a consequence of living in polite society -- we do not 'peek behind the scenes' of what someone is really feeling in most of our polite discourse," he said. "In other words, being polite means seeing someone as they want to be seen, maybe not how they actually are."