You're out with your baby and the pacifier falls on the ground. You pop it in your mouth to "clean" it and give it back to your baby. Can that simple act affect your baby's future allergies?
A recent study offers some evidence that it might. The researchers found that parents who "cleaned" their kids' pacifiers with their own mouths had less allergy-prone kids.
Those children were a little less likely to get asthma or eczema at 18 months old.
Even at age 3, the kids were half as likely to have eczema.
The study, led by Bill Hesselmar, of the Pediatric Allergology and Pediatric Gastroenterology departments of Queen Silvia Children's Hospital in Gothenburg, Sweden, looked for links between children's allergies and how their parents cleaned the kids' pacifiers.
The researchers had conducted interviews with the parents of 184 babies when the children were 6 months old. About 80 percent of the children had at least one parent with allergies.
The interviews included questions about how the parents cleaned the children's pacifiers, which 74 percent of the parents reported their children used in the first six months after birth.
Most of the parents (83 percent) reported they rinsed the pacifier with tap water, and 54 percent of the parents boiled the pacifier.
The researchers found that 65 of the babies' parents "cleaned" the child's pacifier by sticking it in their (parents') own mouth and sucking it briefly.
When the children were 4 months old, the researchers collected saliva samples to analyze the microorganisms in the babies' mouths.
Then, when children were 18 months old and 3 years old, the researchers assessed them for environmental and food allergies.
The researchers did not find a link between a child having a pacifier and the child's development of any allergies.
However, when the researchers looked at the children who had used pacifiers, they found differences based on one parent cleaning method.
At 18 months old, the 65 children of these parents were 12 percent less likely to have asthma and 37 percent less likely to have eczema, compared to the 58 children whose parents did not use their own mouths to clean the pacifiers.
These kids were also 37 percent less likely to test positive on an allergy sensitivity test of different allergens, though this finding could have been due to chance.
The different allergens tested for kids' sensitivity to them included birch, timothy grass, mugwort, cat, dog, horse, mold, house dust mites, milk, egg, soy, fish, wheat and peanut.
The researchers found a slightly higher risk for asthma among the children whose parents boiled their pacifiers, but the increase was so small that it could have been due to chance.
When the children were 3 years old, the ones whose parents cleaned pacifiers with their mouths were still half as likely to have eczema than the children of parents who did not "clean" the pacifier by sucking on it.
When the researchers analyzed the saliva samples of the kids, they found that the make-up of the babies' mouth bacteria differed between the kids whose parents cleaned pacifiers by mouth and the kids whose parents did not use this method.
There was no difference in respiratory infection in the child's first six months based on pacifier cleaning methods, a surprise to Thomas Seman, MD, a pediatrician at North Shore Pediatrics in Danvers, Mass. and a dailyRx expert.
"It was commonly thought that this practice of a parent 'washing off' a pacifier, especially during cold season, would increase the chance of the child getting more frequent viral infections," Dr. Seman said.
"The study interestingly did not show this," he said. "It will be great to see what a follow up study with a larger study group will show."
The parents of babies who were delivered vaginally were more likely to suck their child's pacifier to clean it than children born by cesarean section.
When the researchers controlled for this in their analysis, there was still a lower risk for eczema in the kids whose parents cleaned the pacifier with their mouths. The link for asthma could not be tested because there were not enough asthma cases.
The researchers also found a slightly lower risk of eczema among children who had been born vaginally rather than by cesarean section, separate from the pacifier cleaning method.
The kids born vaginally whose parents cleaned the pacifier by mouth received a double protective effect against eczema: 20 percent of these children had eczema.
Meanwhile 54 percent of children born by C section and whose parents did not use their mouths to clean the pacifier had eczema. Among those who were born vaginally or had their pacifiers cleaned by their parents' mouths, 31 percent had eczema.
"Parental sucking of their infant’s pacifier may reduce the risk of allergy development, possibly via immune stimulation by microbes transferred to the infant via the parent’s saliva," the researchers wrote.
Dr. Seman noted another possible take-home message though — that being dirty can be beneficial sometimes.
"Children should play outside and inside and be allowed to get dirty and enjoy their world," Dr. Seman said. "Children learn and grow when they live and experience the world and all it has to show. An active and varied life creates a healthy child."
The study was published May 6 in the journal Pediatrics. The research was funded by the Swedish Research Council, the Vardal Foundation, the European Commission, the Swedish Asthma and Allergy Association Research Foundation, the Torsten and Ragnar Söderberg Foundation, the Gothenburg Medical Society and the Cancer and Allergy Foundation. The authors declared no conflicts of interest.