The hygiene hypothesis suggests that life activities that introduce early exposure to microbial flora may decrease the risk of allergies as a child gets older. This week that hypothesis gets tested again by looking at thumb-sucking and nail-biting in early childhood and whether infants that do this have a lower risk of atopy, asthma, and hay fever in a study being early released by Lynch et al. (peds.2016-0443).
The authors gathered information from parents in a population-based cohort at ages 5, 7, 9, and 11 and then followed this cohort for allergic findings at age 13 and at age 32 via medical record review of such things as skin testing to document valid allergic findings. As the authors hypothesized, those children who were frequent thumb-suckers and nail-biters had a lower risk of atopic sensitization even when one controls for a variety of possible confounders with the risk being lowest if the child had both habits going for them.
As to asthma and hay fever, no differences were seen. Just why atopic sensitization did show a lower risk and asthma and hay fever did not make for an exciting discussion section of this study—one I guess we could call a real “nail-biter”.
