(Reuters Health) - Parents who pop a pacifier into their mouth to clean it, rather than washing it with soap and water, may be unknowingly reducing their infant’s risk of allergies, new research suggests.

Researchers found that infants whose parents used this technique had lower blood levels of immunoglobulin E (IgE) - a sign of allergic response - over their first 18 months of life.

The results may support previous research suggesting that parental microbes transferred by the pacifier help to boost the baby’s immune system, the study team said November 16 at the American College of Allergy, Asthma & Immunology’s (ACAAI) annual conference in Seattle, Washington.

“The main finding of the research is an association between parents that clean their infant’s pacifier by sucking on it and lower levels of serum IgE antibody,” lead author Dr. Eliane Abou-Jaoude, an Allergy and Immunology Fellow at Henry Ford Health System in Detroit, Michigan, told Reuters Health by email.

There is a big caveat, however.

“Since no cause-effect relationship can be inferred, and there may be unknown potential detrimental effects of pacifier sucking, we would not suggest any clinical relevance or promote this practice based on our findings,” Abou-Jaoude said.

Her team studied data from 128 mother-child pairs participating in a larger study. Blood samples were taken from the children at birth, then at 6 months and 18 months of age. More than half of mothers said their children used a pacifier. Almost three quarters of these mothers said they hand washed the pacifiers, about 40 percent sterilized and 9 percent said they sucked on the pacifier to clean it.

Looking at the serum total IgE levels at birth, 6 months and 18 months, the researchers calculated the trajectory of the natural rise in IgE over time. They found that sterilization and handwashing did not seem to influence IgE levels. But the children of mothers who sucked on a pacifier to clean it had lower total IgE levels, with a statistically meaningful difference from the other babies beginning at age 10 months and the gap widening through age 18 months.

“I thought this study was without-a-doubt eye catching,” said Dr. Neeta Ogden an allergist and immunologist in Edison, New Jersey and ACAAI spokesperson who was not involved in the research.

“It speaks to the hygiene hypothesis, for sure, and our growing understanding that stimulation of the immune system through exposure to a diversity of microbes in an infancy may lead to diminished allergies later in life,” Ogden said.

She echoed the researchers’ cautionary tone, however, saying that the study is limited by its small size and short time period.

“But a great and interesting start,” Ogden said.

SOURCE: bit.ly/2ze2X8H Annals of Allergy, Asthma & Immunology, November 2018.