The emotional development of baby boys may be damaged if they use pacifiers, because using these common objects actually stops babies from experimenting with facial expressions when they are very young.

University of Wisconsin-Madison researchers have associated frequent use of pacifiers with impairing boys' ability to express emotional maturity after conducting 3 separate investigations.

The trial, published in Basic and Applied Social Psychology, is the first of its kind to link psychological outcomes to pacifier use.

In the past, the American Academy of Pediatrics (AAP) and the World Health Organization (WHO) have recommended to control the amount of pacifier use among babies and children. Previous research has determined that stopping the use of pacifiers may encourage feeding. Pacifiers have also been been associated with dental abnormalities. In addition, a 2008 study suggested that there is a link between pacifier use and ear infections.

Paula Niedenthal, lead author of the study and a professor of psychology at UW-Madison, explained:

"By reflecting what another person is doing, you create some part of the feeling yourself. 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."

It has long been known that people of every age imitate the actions of others, including body language, facial expressions, and movements, and these acts of mimicry are very important learning tools for babies to begin expressing their emotions.

Niedenthal continued: "We can talk to infants, but at least initially they aren't going to understand what the words mean. So the way we communicate with infants at first is by using the tone of our voice and our facial expressions."

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When a baby has a pacifier in their mouth, it is difficult for them to be able to copy the actions of the adults or children they are trying to mimic, therefore making it harder for them to learn to express their own emotions.

These results are much like those seen in studies examining the effects of Botox injections, which immobilize the use of facial muscles, and rid the face of wrinkles. Individuals who use Botox have a smaller range of emotions and usually have a hard time recognizing which facial expressions represent certain emotions in others.

"The work got us thinking about critical periods of emotional development, like infancy," said Niedenthal, who has received support for his work from the French Agence Nationale de le Recherche. "What if you always had something in your mouth that prevented you from mimicking and resonating with the facial expression of somebody?"

The authors discovered that boys aged 6 and 7 who used pacifiers regularly as babies or young children were not as likely to copy emotional expression they saw in others in a video they were asked to watch.

Men of college age who self reported using pacifiers often when they were babies had lower scores on tests regarding perspective-taking, a large part of empathy.

The researchers administered a common emotional intelligence test to a group of college students, in order to calculate how the individuals come to conclusions when they are evaluating others' moods. Lower scores were linked to the men who reported the most pacifier use.

"What's impressive about this is the incredible consistency across those three studies in the pattern of data. There's no effect of pacifier use on these outcomes for girls, and there's a detriment for boys with length of pacifier use even outside of any anxiety or attachment issues that may affect emotional development," continued Niedenthal.

The report says that girls may not have these same results from pacifier use because they develop earlier in a variety of ways, suggesting that the girls probably make progress emotionally before pacifier use, or regardless of it. Boys may be more vulnerable than girls, indicating that pacifier use would affect them significantly more.

The idea of pacifier use having such detrimental consequences does not sit well with parents.

The researcher commented:

"It could be that parents are inadvertently compensating for girls using the pacifier, because they want their girls to be emotionally sophisticated. Because that's a girly thing. Since girls are not expected to be unemotional, they're stimulated in other ways. But because boys are desired to be unemotional, when you plug them up with a pacifier, you don't do anything to compensate and help them learn about emotions.

Parents hate to have this discussion. They take the results very personally. Now, these are suggestive results, and they should be taken seriously. But more work needs to be done."

She continued: "Probably not all pacifiers use is bad at all times, so how much is bad and when? We already know from this work that nighttime pacifier use doesn't make a difference, presumably because that isn't a time when babies are observing and mimicking our facial expressions anyway. It's not learning time."

The authors note that the next step in their research is to discover why girls seem to not be affected by pacifier use in the same way boys are, or how they make up for it. Niedenthal calls this type of inspection "dose response".

"I'd just be aware of inhibiting any of the body's emotional representational systems. Since a baby is not yet verbal - and so much is regulated by facial expression - at least you want parents to be aware of that using something like a pacifier limits their baby's ability to understand and explore emotions. And boys appear to suffer from that limitation," concluded Neidenthal

Written by Christine Kearney