Nail biting and thumb sucking are habits most parents try to nip in the bud before they become ingrained habits. But a recent study noted a 30 to 40 percent decrease in the development of allergies among adolescents who had these habits as young children versus those who did not.[Note: as defined by the researchers, “allergies” included both environmental and food allergies, but not hay fever or asthma.]
The results come from a 3-decade research study performed in Dunedin, New Zealand. About 1,000 parents were asked to fill out a questionnaire about their children, and health checks were done at the ages of approximately 13 and 32. The children who were not habitual nail biters or thumb suckers had an increased prevalence of allergies.
The nail biting and thumb sucking correlation was a major revelation. But what does it really mean? At the moment, researchers don’t really have the answers; they merely have another jumping-off point to narrow down the focus of additional studies. However, the results do seem to support the hygiene hypothesis.
What Is the Hygiene Hypothesis?
The hygiene hypothesis essentially states that the more children are exposed to bacteria and microorganisms, the more likely they are to build up a better immune system. It’s a hypothesis borne from the results of other studies that suggest living on a farm, owning pets or even having older siblings allow infants to develop a stronger immune system.
Because nail biters and thumb suckers are more likely to introduce microbes to their systems, transferring whatever was in the environment from their hands to their mouths, perhaps their immune systems were able to develop normal reactions to these foreign invaders, rather than the over-the-top reaction that defines an allergy.
The hygiene hypothesis doesn’t mean that children should never wash their hands, but rather that excessive cleanliness or sterile environments don’t necessarily help in the long run either. And of course, there are detrimental consequences of thumb sucking and nail biting that need to be considered by parents, such as dental problems.
But if scientists can understand what kind of environmental factors provide protective benefits to children, it may be possible to develop allergy preventatives in the future.