Did you happen to catch the report that the children of parents who clean their baby’s pacifier at least some of the time by licking it clean in their own mouths have less allergy than the children of parents who clean the pacifier exclusively by washing it with tap water or sterilizing it in boiling water before returning it to the child’s mouth? Could it be that a parent’s germs are good for preventing eczema and asthma? Who thought to make that observation … and why?
Researchers in allergy, gastroenterology, and infectious diseases/microbiology at the University of Gothenburg in Sweden conducted this study among just over 100 mother/baby pairs. (It has been published in the medical journal, Pediatrics, and you can find it on-line at http://pediatrics.aappublications.org/content/early/2013/04/30/peds.2012-3345). The authors knew of the evidence that when the normal germs that live in the intestines are limited in variety, children are more prone to develop allergies. Among the evidence is the observation that children who are delivered vaginally – and exposed at birth to their mother’s normal vaginal and possibly fecal germs – are less likely to go on to develop allergies than babies delivered by cesarean section in a sterile operating room. The researchers wondered about the potential influence of the normal germs that live in the mouth, and whether by sharing their saliva, parents might expose their babies to a broader array of normal bacteria. The thinking is that if a child’s immune system is exposed to many different types of bacteria at a young age, it will come to accept these foreign substances (antigens) as “friend, not foe” and not attack them using our immune defenses. Exposure to a broad variety of germs appears to “teach” the developing immune system to accept not only these antigens, but also the harmless ones that we identify as allergens, such as cat or dog dander, dust mites, or grass pollens.
In this study from Sweden, most (80%) of the children had at least one parent who was allergic, making it more likely that at least some of the babies would develop allergy. Evidence for allergic disease in the infants was assessed by a pediatrician, based on evidence for sensitization to common allergens on blood testing and the development of asthma or the allergic skin rash, eczema. Their finding? When parents cleaned the pacifier by sucking it, their children were less likely to have eczema and asthma at age 18 months; the odds were reduced by more than 50%. When evaluated again at 36 months of age, the children of parents who cleaned the pacifiers by sucking them still had less eczema, although the differences in rates of asthma and of sensitization to common allergens was no different between the groups.
Two other findings from this study: first, the number of respiratory infections during the first 6 months of life as reported by the parents did not differ between groups; and second, analysis of the babies’ saliva at 4 months, using a sophisticated technique to analyze the presence and variety of bacterial DNA, showed clear differences between children whose parents did and did not use the sucking technique to clean off their baby’s pacifier.
This study taken alone proves very little, and it certainly cannot be taken as a recommendation for preferred child-rearing techniques. But it does add to the growing body of evidence that “too clean” (that is, germ free) may have an undesirable effect on our immune systems, contributing to the ever-increasing prevalence of asthma and allergies in our society. This concept is referred to broadly as the “hygiene hypothesis,” which suggests that reduced exposure of very young children to germs is a risk factor for their development of allergic disease. Other observations like this study of “binkies” provide additional circumstantial evidence about the yin-yang of germs and allergies. For instance, going to daycare at an early age, having older siblings, and growing up in close contact with farm animals all have been shown to lessen one’s chances of developing asthma.
Still ahead is the research that will unravel the exact mechanisms by which the immune system is directed away from allergies when exposed to a broad array of harmless germs at a young age. The potential impact of this understanding is great. Some day one might be able to introduce benign germs of the right type in a way -- at the right age, in the right amount, and over the right period of time – such that one could help prevent susceptible children from developing allergy and asthma. That is the “golden ring” promised by advocates of the hygiene hypothesis.