WASHINGTON — While a lot of parents try to break their children of the habits of sucking thumbs and biting nails at an early age, a recent study says the annoying mannerisms may lead to fewer allergies in adulthood.
The study, led by Professor Bob Hancox at the University of Otago, in New Zealand, and published in the U.S. journal “Pediatrics,” followed the progress of 1,037 participants born in 1972 and 1973 into adulthood.
The findings suggest that childhood exposure to microbial organisms through thumb-sucking and nail-biting reduces the risk of developing allergies down the road.
To measure their habits and allergies, parents of study participants reported their children’s thumb-sucking and nail-biting habits at ages 5, 7, 9 and 11.
At ages 13 and 32, the participants were checked for atopic sensitisation — a positive skin-prick test to at least one common allergen.
The results show that at age 13, 38 percent of those who either sucked their thumbs or bit their nails as a young child showed a sensitivity to at least one allergen, compared with 49 percent of participants who did not practice those habits.
And for those who really had “bad habits” and both bit their nails and sucked their thumbs, only 31 percent showed a sensitivity to allergens. The protection remained when they were tested again at 32 years old, even with adjustments for factors such as sex, parental history of allergies, pet ownership, breast-feeding and parental smoking.
“The findings support the ‘hygiene hypothesis,’ which suggests that being exposed to microbes as a child reduces your risk of developing allergies,” said Hancox.
Despite these findings, Hancox and his co-authors do not suggest that children should be encouraged to take up these habits, because it is unclear if there is a true health benefit.
Researchers found that the protection helps against some allergens, but not all.
“Although thumb-suckers and nail-biters had fewer allergies on skin testing, we found no difference in their risk for developing allergic diseases such as asthma or hay fever,” said Stephanie Lynch, a medical student who undertook the study as a summer project.
