The upside to thumb sucking and and nail biting

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MB-115 thumbsuckChildren who are thumb-suckers or nail-biters are less likely to develop allergic sensitivities,  McMaster University research has found.

And, if they have both ‘bad habits’, they are even less likely to be allergic to such things as house dust mites, grass, cats, dogs, horses or airborne fungi.

And, if they have both ‘bad habits’, they are even less likely to be allergic to such things as house dust mites, grass, cats, dogs, horses or airborne fungi.

The research was completed by researchers of New Zealand’s Dunedin School of Medicine, assisted by professor Malcolm Sears of McMaster University’s Michael G DeGroote School of Medicine.

“Our findings are consistent with the hygiene theory that early exposure to dirt or germs reduces the risk of developing allergies,” said Sears, who is formerly of Dunedin and also a researcher for the Firestone Institute for Respiratory Health at McMaster and St Joseph’s Healthcare Hamilton. “While we don’t recommend that these habits should be encouraged, there does appear to be a positive side to these habits.”

The researchers were testing the idea that the common childhood habits of thumb-sucking and nail-biting would increase microbial exposures, affecting the immune system and reducing the development of allergic reactions also known as atopic sensitisation.

The habits of thumb-sucking and nail-biting were measured in a longitudinal birth cohort of more than 1,000 New Zealand children at ages 5, 7, 9 and 11; and atopic sensitisation was measured by skin-prick testing at 13 and 32 years old.
The researchers found 31% of children were frequent thumb suckers or nail biters.

Among all children at 13 years old, 45% showed atopic sensitisation, but among those with one oral habit, only 40% had allergies. Among those with both habits, only 31% had allergies. This trend was sustained into adulthood, and showed no difference depending on smoking in the household, ownership of cats or dogs; or exposure to house dust mites.

However, the study did not find associations between the oral habits and development of asthma or hay fever.

Abstract
Background: The hygiene hypothesis suggests that early-life exposure to microbial organisms reduces the risk of developing allergies. Thumb-sucking and nail-biting are common childhood habits that may increase microbial exposures. We tested the hypothesis that children who suck their thumbs or bite their nails have a lower risk of developing atopy, asthma, and hay fever in a population-based birth cohort followed to adulthood.
Methods: Parents reported children’s thumb-sucking and nail-biting habits when their children were ages 5, 7, 9, and 11 years. Atopic sensitization was defined as a positive skin-prick test (≥2-mm weal) to ≥1 common allergen at 13 and 32 years. Associations between thumb-sucking and nail-biting in childhood, and atopic sensitization, asthma, and hay fever at these ages were assessed by using logistic regression with adjustments for sex and other potential confounding factors: parental atopy, breastfeeding, pet ownership, household crowding, socioeconomic status, and parental smoking.
Results: Thirty-one percent of children were frequent thumb-suckers or nail-biters at ≥1 of the ages. These children had a lower risk of atopic sensitization at age 13 years (odds ratio 0.67, 95% confidence interval 0.48–0.92, P = .013) and age 32 years (odds ratio 0.61, 95% confidence interval 0.46–0.81, P = .001). These associations persisted when adjusted for multiple confounding factors. Children who had both habits had a lower risk of atopic sensitization than those who had only 1. No associations were found for nail-biting, thumb-sucking, and asthma or hay fever at either age.
Conclusions: Children who suck their thumbs or bite their nails are less likely to have atopic sensitization in childhood and adulthood.

Authors
Stephanie J Lynch, Malcolm R Sears, Robert J Hancox

McMaster University material
Paediatrics abstract


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