Does thumb sucking ward off allergies?

Children who suck their thumbs or bite their nails may have a lower risk of developing allergies, according to new findings published in the journal Pediatrics.

“While we don’t recommend that these habits be encouraged, there does appear to be a positive side to them,” states AllerGen investigator Dr. Malcolm Sears, a co-author of the paper and Professor of Medicine at McMaster University, where he holds the AstraZeneca Chair in Respiratory Epidemiology.

“Thumb-sucking and nail-biting are common habits that have the potential to increase a child’s exposure to environmental microorganisms,” Dr. Sears explains, which, in turn, can “influence the immune system in making it more tolerant to allergens.”

This finding adds to the growing evidence in support of the hygiene hypothesis: that early childhood exposure to common germs strengthens the body’s immune system, and thus being brought up in an overly hygienic environment can increase one’s vulnerability to allergies later in life.

The research uses data from the Dunedin Multidisciplinary Health and Development Study—a New Zealand-based birth cohort study initiated in the early 1970’s, for which Dr. Sears was the original leader of the asthma and allergy component.

The present study tracked the health status of more than 1,000 individuals at various ages from five to 32 years, testing them for sensitivity to various common allergens, including cats, dogs, horses, house dust mites and grasses. The researchers found that childhood thumb-suckers and nail-biters were less likely to show signs of allergic sensitization to these allergens as teens or adults. However, these hand-mouth habits did not appear to affect their risk of developing asthma or hay fever.

”The bottom line, I would say, is that what the paper tells us is that a little exposure to dirt is not necessarily a bad thing,” Dr. Sears concludes.

The study has been reported widely by media including the BBC, The Telegraph, The New York Times, TIME, The Globe & Mail, The Washington Post and CBC.

Dr. Sears leads AllerGen’s birth cohort study–the Canadian Healthy Infant Longitudinal Development (CHILD) Study—which is also investigating the early life origins of asthma, allergies and other diseases.