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They're habits that many parents try to discourage in their children, but a New Zealand study out Monday shows that thumb-sucking and nail-biting could lead to fewer allergies in later life.
The University of Otago finding emerged from a long-running study that followed the lives of 1,037 New Zealanders born in 1972 and 1973.
It found childhood exposure to microbial organisms through thumb-sucking and nail-biting might alter immune function so that children became less prone to developing allergies, study lead author Professor Bob Hancox said in a statement.
Parents of the study members reported their children's thumb-sucking and nail-biting habits when their children were aged 5, 7, 9 and 11 years old.
They were checked at ages 13 and 32 years old for atopic sensitization, defined as a positive skin prick test to at least one common allergen.
At age 13, the prevalence of sensitization was lower at 38 percent among children who had sucked their thumbs or bit their nails compared with those who did not at 49 percent.
Children who both bit their nails and sucked their thumbs had an even lower risk of allergy at 31 percent, said Hancox.
The associations were still present at age 32 and persisted even with adjustments for confounding 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," he said.
Despite these findings, Hancox and his co-authors did not suggest that children be encouraged to take up the habits, because it was unclear if there was a true health benefit.
"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," researcher Stephanie Lynch said in the statement.
(APD)
