There's an evolutionary explanation for most behaviors, and nail-biting is no exception. A new study in Pediatrics has shown nail-biting and thumb-sucking - two pretty effective ways of exposing oneself to environmental microbes - are associated with lower rates of positive skin-prick tests, or atopic sensitization.
The study included data from 724 children in New Zealand who underwent skin-prick testing at ages 13 and 32 as part of the longitudinal population-based Dunedin