That old-fashioned way of cleaning your baby's pacifier with your own saliva could transfer germs that actually help boost the infant's immune system and stave off allergies, according to a recent study by Swedish researchers.
But the study is also drawing criticism from some dentists and doctors who say that oral bacteria could increase the risk of cavities or infectious diseases.
Researchers examined 184 infants for allergies at 18 and 36 months, also recording pacifier use and cleaning methods at six months, in the study, which was published in the June issue of Pediatrics.
The 65 babies whose parents sucked on the pacifiers to clean them were 88 percent less likely to have asthma and 63 percent less likely to have eczema or show desensitization at 18 months than those whose parents used other cleaning methods. The benefit for eczema remained at 36 months.
The researchers also found that the babies who were delivered vaginally and whose parents sucked on the pacifiers to clean them had the lowest prevalence of eczema, at 20 percent. The authors said vaginal delivery might have helped protect against allergy by exposing the babies to bodily fluids and allowing them earlier discharge from the hospital than their counterparts delivered by cesarean section.
The American Dental Association criticized the study, saying saliva sharing should be avoided because it spreads bacteria and promotes tooth decay.
"Tooth decay remains the most common chronic disease of childhood," said Dr. Jonathan Shenkin, a pediatric dentist and spokesman for the association. "It causes pain, school loss, attention problems and sets you up for a lifetime of tooth decay.
The issue of pacifier cleaning needs further study before parents can make an informed decision, Shenkin said.
Dr. Bill Hesselmar, a lead author of the study, said in an email that other studies showed no link between pacifier use and cavities. So, because both pacifier use and cleaning with saliva are common, an increase in cavities would hypothetically follow if saliva caused tooth decay, said Hesselmar, an associate professor at Queen Silvia Children's Hospital in Gothenberg, Sweden.
Hesselmar noted that some studies showed saliva may contain protective agents against cavities. But he agreed the results need to be replicated on a larger scale before recommendations could be made either way.
Dr. Renee Slade, a pediatrician at Rush University Medical Center, said increased exposure to some germs can have health benefits, citing the Hygiene Hypothesis. That theory contends that when children are exposed to more bacteria and some infections, they have a decreased risk of asthma.
But Slade also cautioned against sharing saliva because of possible increased tooth decay. She pointed out that mothers could decrease the risk of allergies through breast feeding.
"I'm not ready to recommend that parents suck on their babies pacifiers at this point in time," said Slade, also noting the limited size of the Swedish study. "If parents have cavities or are prone to them, I would for sure not recommend that they suck on babies' pacifiers."