After all, children teased for sucking their thumb or biting their nails may have the last laugh.
It turns out that repeatedly sticking grubby digits in your willy as a youngster can help boost your immune system and prevent the development of allergies later in life, researchers report in the August 2010 issue of Pediatrics. The finding is certainly a score for the schoolyard underdogs, but also lends more support to the “hygiene hypothesis.” This decades-old hypothesis generally suggests that exposure to germs and harmless microbes in childhood can help develop a healthy, tolerant immune system, that is, an immune system that is not susceptible to autoimmune diseases and hypersensitive reactions such as allergies.
“While we are not suggesting that children should be encouraged to adopt these oral habits, the findings suggest that thumb sucking and nail biting reduce the risk of developing hypersensitivity to common aeroallergens,” the study authors concluded.
The researchers, led by Stephanie Lynch of New Zealand’s Dunedin School of Medicine, came up with the idea after reports that babies whose mothers licked their pacifiers clean were less likely to develop asthma and eczema. Thumb sucking and nail biting could have the same effect, they reasoned.
Lynch and colleagues examined data from the Dunedin Multidisciplinary Health and Development Study, which had followed 1,037 children born in Dunedin, New Zealand, between 1972 and 1973. In that study, parents were surveyed about their children’s thumb sucking and nail biting. ways the children were 5, 7, 9 and 11 years old. Most children also received skin prick allergy testing at ages 13 and 32. Those tests looked for reactions to common allergens, such as house dust mites, grass pollen, cats, dogs, horses, wool and everyday molds. The researchers also gathered information on other factors that may influence the development of allergies, including breastfeeding, cat and dog ownership, parental smoking and allergies, busy living conditions and socioeconomic status.
According to the answers to the parent survey, 31 percent of children were “frequent” finger nibblers — nail biters, thumb suckers, or both — somewhere between the ages of 5 and 11.
At age 13, 724 children took the skin prick test, and 45 percent of them had at least one allergy. But when the kids were sorted out, those with oral habits fared better. Of the kids who didn’t suck their thumb or bite their nails, 49 percent had allergies. Of the kids who had one of those mouth habits, 41 percent had allergies. And of the kids who did both, 31 percent had allergies.
At age 32, 946 of the children – now adults – took the skin test again. The results were similar, except that at this age, the participants who had both childhood oral habits fared about the same as those who had only one. Still, the results held up: Putting germ fingers in your mouth as a child seemed to reduce the risk of allergies later in life by about 30 to 40 percent. And the results held up even after researchers controlled for the other allergy-altering environmental and genetic factors.
However, the researchers also looked at whether finger chewing in general reduced the incidence of asthma and hay fever and found no association. They will need to do more research with other groups of children to validate the results and try to understand how the unsanitary habit may affect some allergies and not others.
Finally, the authors note that finger biting and thumb sucking have been linked to problems other than schoolyard bullying, such as tooth misalignment and finger infections. But if the study is correct, these “bad habits” may not all be bad.
Pediatrics2016. DOI: 10.1542/peds.2016-0443 (About DOIs).