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.
