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(CNN)Your baby's pacifier falls on the floor. Before giving it back to your child, do you wash it in a sink or, perhaps reluctantly, clean it with your own saliva?
Don't feel too guilty if you chose the latter, because a new study suggests that a mother's spit -- and the bacteria in it -- may help prevent allergies in young children.
The research found lower levels of a troublesome, allergy-causing protein in babies whose mothers reported sucking on their infants' pacifiers, adding to a growing body of evidence that early exposure to microbes may prevent allergies in children.
"The idea is that the microbes you're exposed to in infancy can affect your immune system's development later on in life," said Dr. Eliane Abou-Jaoude, an allergy fellow with the Henry Ford Health System in Detroit. She is presenting her findings this weekend at the American College of Allergy, Asthma, and Immunology Annual Scientific Meeting.
Microbial exposure might prevent allergies
Research has shown that people who live near livestock, those who avoid dishwashers and babies born through the microbe-filled vaginal canal -- instead of via C-section -- are all less likely to develop allergies.
The new study, which hasn't been peer-reviewed, is "one more piece of data that early exposure to microbes helps prevent allergies," said Dr. Andrew MacGinnitie, clinical director of the Division of Immunology at Boston Children's Hospital.
But the study has weaknesses as well, MacGinnitie said. It has a small sample size, making it difficult to draw too many conclusions, and factors other than the mother's saliva could have helped develop the children's immune systems.
"It's possible that sucking on a pacifier is correlated with other, more important factors that predispose or protect against allergens," he said, adding that mothers who suck on their children's pacifiers could also "let their kids play in the dirt, or their whole house could be less clean."
Uncertainty over causation is why Abou-Jaoude isn't recommending that parents start sucking on their children's pacifiers just yet.
"What's very, very important to realize is that this was not a cause and effect study," she said. "This is not telling you, if you suck on your child's pacifier, they will not develop allergies."
For those who choose to do so, though, MacGinnitie doesn't see too many risks. "If the kid were sick, he or she could transmit an infection to the mom or dad, but if the kid is well, this would seem to be unlikely," he said.
And even if the pacifier falls on the floor, he added, "in general, the bacteria and viruses on the floor don't cause disease."
A decrease in allergy-linked proteins
To determine allergy risk, researchers looked for a protein linked to allergies. They tracked levels of that protein, the IgE antibody, in 74 infants whose mothers reported using pacifiers. No fathers were included in the research.
Just nine babies had mothers who sucked their children's binkies clean. But compared with the other children, those nine babies had significantly lower levels of IgE antibody, a trend that began when the children were about 10 months old.
The researchers tracked the babies for only 18 months, making it unclear whether lower IgE levels in infancy would translate to fewer allergies later in life.
"Based on these levels, you can't really tell what's going to happen to these kids in the future," Abou-Jaoude said. "All is we know is, people with allergies, they usually have higher levels of IgE antibodies. But that doesn't mean that if you have high IgE, you're definitely going to have allergies."
Our bodies develop antibodies to fight infections, but MacGinnitie said IgE antibodies are often produced in response to harmless substances -- which is why they're closely associated with allergies.
"Allergies are an inappropriate response by our immune system to see something that's innocuous as dangerous," he said, leading to congestion, hives and other common symptoms.
Reducing your child's allergy risk
Abou-Jaoude's team looked at total IgE antibody levels, but researchers can also test for allergen-specific IgE levels, looking at how sensitive a child might be to particular substances, like eggs or dogs.
A 2013 study in Sweden did just that. Not only did researchers find that infants were less likely to have IgE antibodies against common allergens when their parents sucked their pacifiers, but they were also less likely to develop eczema and asthma by the time they were 18 months old.
"If I understand the paper and the figure correct, [the new study] found lower IgE levels in children whose parents reported sucking on their pacifier, and that finding supports our results," said Dr. Bill Hesselmar, an associate professor in pediatrics at the University of Gothenburg who authored that study.
In both cases, Hesselmar says, sucking on a baby's pacifier might have transferred "microbes that could stimulate the immune system so that tolerance develops instead of allergy."
Still, there are more practical -- and perhaps more pleasant -- ways to prevent allergies in children. MacGinnitie said that early exposure to some foods, for example, may protect against allergies.
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Studies have shown that "kids introduced to peanuts in the first year of life have a much lower chance of developing a peanut allergy," he said, and the American Academy of Pediatrics agrees. In 2017, the group endorsed guidelines recommending that infants at high risk for allergies start eating peanuts as early as 4 to 6 months of age.
Children who grow up with pets also tend to have a lower allergy risk, MacGinnitie said, but that might be explained by genetics. In other words, allergy-free parents who own pets might just give birth to allergy-free kids.
"Living on a small farm also probably helps," MacGinnitie joked. But he added that, for most parents, "that's probably not realistic."
