A recent study published in Developmental Science has discovered a connection between prolonged pacifier use and reduced vocabulary size in infants at both 12 and 24 months of age. The study indicates that extended use of pacifiers may negatively impact language development, with later pacifier use showing a stronger association with smaller vocabulary sizes compared to earlier use.
The use of pacifiers is widespread among young children across the globe, often valued for their soothing effects on infants. While pacifiers are recommended by health organizations for reducing the risk of sudden infant death syndrome (SIDS) and can provide comfort, concerns have emerged regarding their potential impact on a child’s development, particularly language acquisition.
Previous research has mainly focused on the physical impacts of pacifier use, such as dental misalignments and increased risk of ear infections. However, the potential effects on language development have received less attention. This study aimed to fill that gap by investigating whether sustained pacifier use could disrupt early speech perception and language development by restricting the movements of the mouth and tongue.
“Our interest was sparked by a study by Bruderer et al. (2015) showing that infants had difficulty distinguishing sounds when their tongues were blocked by a teether. We wanted to investigate if prolonged pacifier use might eventually lead to differences in how quickly children learn words,” explained study author Luis Eduardo Muñoz, a PhD candidate at the University of Oslo.
For their study, the researchers recruited parents of infants from Oslo, Norway, through birth registries, covering the period from 2019 to 2020. Initially, the study included 1,630 participants, but after applying specific inclusion criteria, such as monolingual exposure to Norwegian, being born full-term, and having no reported visual, auditory, or cognitive impairments, the final sample consisted of 1,187 infants.
To assess vocabulary size, parents completed an online questionnaire that included the Norwegian versions of the Communicative Development Inventories (CDIs). For 12-month-old infants, the CDIs measured both vocabulary comprehension and production, while for 24-month-olds, it measured vocabulary production only. Comprehension refers to the ability of infants to understand and recognize words when they hear them, while production refers to the ability to actively use words in speech.
Parents also provided detailed reports of their child’s daytime pacifier use. They retrospectively estimated the average daily use in whole hours for two-month intervals from birth until the assessment date. This allowed the researchers to calculate the total hours of pacifier use over the infants’ lifetimes, referred to as Lifespan Pacifier Use (LPU).
The researchers uncovered a significant negative association between sustained pacifier use and vocabulary size in both 12- and 24-month-old infants. Specifically, for 12-month-olds, an increase in pacifier use by one standard deviation (about 1.8 hours daily) was linked to a reduction in vocabulary comprehension and production percentiles by 2.9 and 2.6 percentiles, respectively. For 24-month-olds, a similar increase in pacifier use corresponded to a 2.4 percentile decrease in vocabulary production.
The researchers also explored how changes in pacifier use over time influenced vocabulary development. They found that infants with increasing pacifier use as they aged had lower vocabulary sizes compared to those with declining or stable pacifier use. This effect was observed even after controlling for the total amount of pacifier use.
Notably, the impact of pacifier use was stronger when it occurred later in infancy. For instance, 24-month-olds with higher pacifier use between 18 and 24 months were 3.6 percentiles lower in vocabulary production compared to their peers.
Further analysis focused on the most recent period of pacifier use before the infants’ second birthday. The results showed that greater pacifier use between 22 and 24 months increased the likelihood of infants scoring in the lower 15th percentile for vocabulary size at 24 months. Specifically, an increase of one standard deviation in pacifier use during this period raised the odds of being in the lower percentile by a factor of 1.4.
“We found it interesting that recent pacifier use (within the last two months) had the strongest link to smaller vocabulary sizes, indicating the potential significance of the most recent amount of pacifier use,” Muñoz told PsyPost.
However, it is important to note that the study’s design does not allow for establishing a causal relationship between pacifier use and vocabulary development. The study is cross-sectional, meaning it looks at data from a single point in time rather than following the same children over an extended period.
While this can show associations or correlations between variables, it cannot determine whether one factor directly causes another. In other words, while the study found a link between prolonged pacifier use and smaller vocabulary sizes, it cannot definitively say that pacifier use causes reduced vocabulary development.
“Our study doesn’t provide evidence that pacifiers themselves cause slower word learning, but it does suggest a link between frequent pacifier use and smaller vocabularies at ages 1- and 2-years-old,” Muñoz explained. “There could be many other factors at play, such as parenting styles or the child’s temperament.”
To better examine the potential for causality, researchers could conduct longitudinal studies, which track the same group of children over several years. This approach allows researchers to observe how changes in pacifier use over time might influence vocabulary development.
“We aim to further explore how pacifier use, parenting styles, and children’s temperament interact to affect word learning,” Muñoz said. “Pacifier use is a culturally sensitive topic, and we don’t want this study to stigmatize parents who use them. There are valid reasons for pacifier use (soothing), and our findings should not be taken as a reason to discourage it.”
The study, “Sustained pacifier use is associated with smaller vocabulary sizes at 1 and 2 years of age: A cross-sectional study,” was authored by Luis E. Muñoz, Natalia Kartushina, and Julien Mayor.
