NEW YORK (CBS NEWS) – New research suggests pacifier use may have long-lasting behavioral effects on a boy’s emotional growth.

Three separate experiments — two with college-aged students and one with 6-to-7-year-old boys — revealed that those who reported using pacifiers found it harder to mimic emotional expressions or scored lower on emotional intelligence tests. The study is the first to connect pacifiers with psychological effects.

“That work got us thinking about critical periods of emotional development, like infancy,” lead author Dr. Paula Niedenthal, a psychology professor at the University of Wisconsin in Madison, Wisc., said in the press release. “What if you always had something in your mouth that prevented you from mimicking and resonating with the facial expression of somebody?”

According to the researchers, people mimic expressions and body language either consciously or unconsciously. Mimicking can teach them what certain words mean through facial expressions and voice intonations, which is specially in babies.

“By reflecting what another person is doing, you create some part of the feeling yourself,” Niedenthal said. “That’s one of the ways we understand what someone is feeling – especially if they seem angry, but they’re saying they’re not; or they’re smiling, but the context isn’t right for happiness.”

But, the researchers believe when a baby has a pacifier in his or her mouth, they can’t copy the expressions or emotions they are feeling. Similar experiences have been displayed in people who use Botox. Those who use the treatment report a smaller range of emotions and have a harder time labeling emotions on other people’s faces.

The Mayo Clinic adds that pacifiers, while they can soothe babies and help them fall asleep, can also cause problems with breast-feeding, increase the risk of middle ear infections and lead to dental problems. In addition, children who use pacifiers to sleep may become dependent on them.

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