The hygiene hypothesis has been a popular explanation for many aspects of allergic disease in children. A recent birth cohort study from Sweden has found additional data to support this hypothesis. In a birth cohort at risk of allergic disease (on the basis of family history), infants whose parents cleaned the infant's pacifier (‘dummy’) by sucking had a significantly reduced risk of allergic disease at both 18 months and 36 months. A total of 65 parents cleaned their infant's pacifier by sucking, while 58 parents used other cleaning methods (usually rinsing with tap water). The rate of asthma at 18 months was significantly lower in the ‘parental sucking’ group than the ‘non-sucking group’, with an odds ratio (OR) of 0.12 (confidence interval (CI) 95% = 0.01–0.99). The rate of eczema was also significantly reduced, OR = 0.37 (CI 95% = 0.15–0.91). Allergic sensitisation was also reduced, OR = 0.37, but not significantly (CI 95% = 0.10–1.27). At 36 months, the protection in the ‘parental sucking’ group remained significant for eczema only (hazard ratio = 0.51, P = 0.04). The authors suggest this protection is due to immune stimulation by the bacteria transferred to the infant via the parent's saliva. Interestingly, vaginal delivery (vs. caesarean) and ‘parental pacifier sucking’ were independently associated with protection and gave additive protection against eczema. Although this is a small study, with wide confidence intervals, it warrants further study.
Reviewer: Craig Mellis, firstname.lastname@example.org