Many parents rely on pacifiers to calm and settle babies and sometimes even toddlers.
But according to new research, pacifiers, also known as dummies, could stunt the emotional development of baby boys by inhibiting them from trying facial expressions during infancy.
Interestingly the same is not true for baby girls, say the US researchers.
The World Health Organisation and the American Academy of Paediatrics have already called for decreased pacifier use to promote breastfeeding, and to limit ear infections or dental abnormalities.
This new study by psychologists from the University of Wisconsin-Madison is the first to associate pacifiers with psychological consequences.
The researchers, led by Dr Paula Niedenthal, a psychology professor at the university, say humans of all ages often mimic the expressions and body language of people around them.
“By reflecting what another person is doing, you create some part of the feeling yourself,” says Niedenthal. “That’s one of the ways we understand what someone is feeling â€” especially if they seem angry, but they say they’re not; or are smiling, but the context isn’t right for happiness.”
According to Niedenthal, mimicry can be an important learning tool for babies. “We can talk to infants, but at least initially, they are not going to understand what the words mean,” she says.
“So the way we communicate with infants at first is by using the tone of our voice as well as our facial expressions.”
Babies who suck on pacifiers are less able to mirror those expressions and emotions. The effect is similar to those of patients receiving Botox, to paralyse facial muscles and reduce wrinkles, she says.
“That work got us thinking about critical periods of emotional development, such as infancy,” says Niedenthal.
“What if you always had something in your mouth preventing you from mimicking and resonating with the facial expression of somebody?”
Less likely to mimic emotional expressions
The researchers discovered that six-and seven-year-old boys who spent more time with pacifiers in their mouths as young children were less likely to mimic the emotional expressions of faces shown on a video.
Young men who reported high pacifier use as children, scored lower than their peers on common tests of perspective-taking, which is a component of empathy.
In another study, a group of university students took a standard test of emotional intelligence measuring the way they made decisions based on assessing the moods of other people. Heavier pacifier use went hand-in-hand with lower scores.
“What’s impressive about this is the consistency across those three studies in the pattern of data,” Niedenthal says.
“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.”
The gender divide
To explain the gender divide, Niedenthal says girls develop earlier in many ways, and it is possible that they make sufficient progress in emotional development before or despite pacifier use. Or it may just be that boys are more vulnerable than girls, and disrupting use of facial mimicry is more detrimental.
“Parents could be inadvertently compensating for girls using the pacifier,” Niedenthal says.
Suggesting that such a simple and common act as pacifier use has lasting and serious consequences is far from popular.
“Parents hate to have this discussion,” Niedenthal says.
“They take the results very personally. These are suggestive results, and they should be taken seriously, but more work needs to be done.”
Investigating why girls seem to be immune (or how they may compensate) is an important next step, as is an investigation of what Niedenthal calls “dose response”.
“Probably not all pacifier use is bad at all times, so how much is bad and when?” she says.
“We already know from this work that night-time 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.”
“A baby is not yet verbal â€” and so much is regulated by facial expression â€” so at least you want parents to be aware that a pacifier can limit their baby’s ability to understand and explore emotions. And boys appear to suffer from that limitation,” Niedenthal says.