Admit it, you've done this: your kid drops her pacifier on the floor and, too exhausted to schlep to the kitchen sink to rinse it, you just give it a good lick and hand the binky back.
Well, it turns out this not-so-pretty cleaning method you turn to when no one else is looking may, in fact, be one helluva gift for your child's immune system.
Researchers in Sweden report that "children whose parents sucked on their pacifiers to clean them had one-third the risk of developing eczema (the most common early manifestation of allergy), at 18 months of age, compared to children whose parents did not use this cleaning practice."
It gets better. Infants who were born vaginally and were lucky enough to have a parent suck clean his or her pacifier got an added boost, the study found: "The prevalence of eczema was approximately 2.5 times lower at 18 months of age in vaginally delivered children whose parents sucked their pacifiers than in caesarean section-delivered children whose parents did not have this habit (20% vs. 54%)," the study says.
The takeaway from the study, published online today in the journal Pediatrics, is this: It looks like early exposure to parents' saliva may help stimulate a baby's immune system,
and that could mean a lower risk of developing eczema, asthma and sensitivities to certain allergens. The study authors suggest that healthy oral flora is the key here and that the "transfer of oral microbes from parent to infant via the pacifier might be used in primary prevention."
"It is a support for the hygiene hypothesis, that early microbial exposure is important for normal tolerance development," lead author Bill Hesselmar, an associate professor at Queen Silvia Children's Hospital in Gothenburg, Sweden, says via email.
And it's not only the oral microbes that appear to be protective here.
In a discussion on why parents of children born vaginally appear to be more inclined to lick their children's pacifiers, the authors speculate that the very nature of the birth itself — the wet, messy reality of vaginal birth compared to the medical sterility of a caeseran section — might somehow be internalized by new parents.
During a vaginal delivery, the baby is exposed to bodily fluids and sometimes soiled with faeces; after a normal delivery the mother and baby will be speedily discharged from the hospital. In contrast, delivery by caesarean section is a strictly sterile surgical procedure followed by hospital stay and substantial medical attention. Theoretically, the ‘sterility culture’ of the hospital may be transmitted to the parents and influence their subsequent care of their baby even when they return home.
In any case, the message is clear. Familial saliva sharing sure looks like a good thing.
And, says Moises Velasquez-Manoff, author of the book, “An Epidemic of Absence: A New Way of Understanding Allergies and Autoimmune Diseases,” "It's completely consistent with the accumulating evidence suggesting that there are microbes transmitted from parents to children that are good for us."
He suggests: "Think of it as your inherited microbial wealth — like heirlooms --you need to get them from other humans and the most likely source is from your parents when you're young."
When you interrupt that important transfer of microbes, Velasquez-Manoff says, the immune system can get out of whack. In his book, which might also be called, "beyond the hygiene hypothesis," he argues that modern humans have sanitized out of our lives many critical parasites and microbes that we co-evolved with. As a result, our immune systems have become unable to properly regulate themselves, and we are suffering from a myriad of inflammation-related disorders such as allergies and asthma, but also possibly, as he recently suggested in The New York Times, from autism, because of this sub-optimal immune response.
As far as the pacifier-licking study, Velasquez-Manoff says it may not only be the microbes at work here. "Saliva also has antibodies in it, and if we're healthy, the antibodies in our saliva send the message to tolerate this." He offers the example of premastication, noting that before infants ate food from cans and jars, mothers simply pre-chewed food for their babies to eat.
"You transfer both the good microbes and antibodies when you do that," he said. "But that began changing in the upper classes in the 19th century — and even earlier — when there was a culturally taught disgust toward bodily fluids. That happened with growing affluence."
The Swedish pacifier study was fairly small, 184 infants, examined at 18 months and again at 36 months. Here are details:
A birth-cohort of 184 infants was examined for clinical allergy and sensitization to airborne and food allergens at 18 and 36 months of age and, in addition, promptly on occurrence of symptoms. Pacifier use and pacifier cleaning practices were recorded during interviews with the parents when the children were 6 months old. The oral microbiota of the infants was characterized by analysis of saliva samples collected at 4 months of age.
Children whose parents “cleaned” their pacifier by sucking it (n = 65) were less likely to have asthma (odds ratio [OR] 0.12; 95% confidence interval [CI] 0.01–0.99), eczema (OR 0.37; 95% CI 0.15–0.91), and sensitization (OR 0.37; 95% CI 0.10–1.27) at 18 months of age than children whose parents did not use this cleaning technique (n = 58). Protection against eczema remained at age 36 months (hazard ratio 0.51; P = .04).
Clearly, more research and a larger study is needed to know precisely the mechanism at work here.
Velasquez-Manoff says it would have been interesting to know what was in the house — a pet, for instance — to figure out if people licking the pacifier after dropping it on the floor might have had a more diverse microbiota. "It would have been nice to know what else these mothers were exposed to during pregnancy," he said.
Still, the practice of licking your children's objects clean probably can't hurt, he says: "I don't see anything wrong with parents sharing saliva with children. They're getting it anyway, right? Your kid is all over you."
This program aired on May 6, 2013. The audio for this program is not available.