Do Thumb-Sucking and Nail-Biting Protect Against Allergy?

By Christine Judge

Edited by Susan Sadoughi, MD, and André Sofair, MD, MPH

Thumb-sucking or nail-biting in childhood is associated with reduced risk for later atopic sensitization but not asthma or hay fever, a Pediatrics study suggests.

The parents of roughly 1000 New Zealand children reported on their children's oral habits at ages 5, 7, 9, and 11 years. Skin-prick testing for selected antigens was conducted in most participants at ages 13 and 32, at which time asthma and hay fever were self-reported.

Some 31% of children were thumb-suckers or nail-biters at one or more ages. These children had about a 35% reduction in atopic sensitization at age 13 and nearly a 40% reduction at age 32. Neither habit was tied to risk for asthma or hay fever.

In NEJM Journal Watch Pediatrics and Adolescent Medicine, Dr. John C. Cowden says: "We should bear in mind that atopic sensitization is not synonymous with allergic disease. Though the relationship between oral habits and sensitization is interesting, there was no association between oral habits and disease ... and thus no clear evidence of clinical benefit. That does not mean one does not exist, but for the primary care clinician, this study should be taken as a primarily negative result, with a curious positive finding on the side."