Years ago, when my children (now teenagers) were babies and they dropped a pacifier on the floor, we rinsed it with tap water before putting it back in their mouth.

As a parent and as an infectious disease doctor, sterility is of utmost importance to me. While this may be lifesaving in the hospital, it may not be the best practice at home, according to a recent study in the journal Pediatrics.
A group of Swedish scientists found that if parents cleaned their child’s pacifier by sucking on it before placing it back in the child’s mouth, the child was significantly less likely to have allergies at 18 and 36 months.
Children of pacifier-sucking parents (I guess we can call them that) had nearly 60 percent less eczema and 90 percent less asthma by 18 months compared to parents who used tap or boiling water.

How can this be? Isn’t cleanliness the best option? Aren’t bacteria our foe? Shouldn’t we all be using hand sanitizer multiple times in a day?

The answer is a bit complex. Humans and bacteria have had both an adversarial and symbiotic relationship since the start of time. Bacteria colonize our skin, our mouth, and our intestines, mostly the colon. The bacterial flora in our bodies, also called the microbiome, change with what we eat, where we live and what we put in our mouths.
So when children receive the pacifier with their parent’s spit, they also receive the harmless bacteria from their parent’s mouth. Once the bacteria are in the baby’s mouth and gut, they create an immune response — creating antibodies that help protect the child from future bacterial invasions. Stimulation and exposure to bacteria at an early age lead to less eczema and allergies, which are immune-mediated diseases.
So, during breakfast, after hearing about the study on National Public Radio, I touted the benefits of families “sharing” bacteria. That is when my high-school daughter, who was recovering from a cold, promptly went within 3 feet of my middle-school son’s face and coughed on him. I rebuked her. “Sharing of good bacteria is OK — not of other pathogens that can cause an illness.”

So should we change our practices? Should parents lick or suck the pacifier before sticking it in their babies’ mouths? Not so fast, say many scientists. It may be that the parents who cleaned the pacifier with tap water or by boiling may have had common characteristics such as unclean homes or history of smoking that may lead to higher rates of allergies in children. However, when the researchers adjusted for some of the confounding variables, they found no difference.
On the other hand, I don’t think we need to be so obsessive and compulsive about cleanliness in the household setting. Studies show that children who grow up on farms are less likely to have allergies than those who grow up in cities. Researchers suspect this may be due to exposure to multiple organisms at an early age, possibly a dirtier environment on the farm.

In the Swedish study, when the researchers looked at the impact of vaginal delivery, which exposes the baby to the bacteria in the mother’s vaginal canal at delivery, versus cesarean section (a sterile procedure), those born vaginally had an even lower rate of allergies.
Again, the theory is that the bacteria likely stimulate the immune system of babies, and so later in life when the child is exposed to pollen, cats and peanuts, the immune system does not overreact. Ultimately, this reduces the risk of allergies and eczema.

So, I told my wife: “I couldn’t do it. Sucking a pacifier that has dropped on the floor and then placing it in my child’s mouth, that’s so yucky.”

My son couldn’t resist the one-liner: “Suck it up, Dad.”