Parents who’ve struggled and failed to get their youngsters to quit thumb sucking can take heart: there may be an upside to the habit. Researchers have found thumb sucking and nail biting in young children may be protective against allergies.
Compared to children with neither habit, those who sucked their thumbs and bit their nails were far less likely to develop sensitivities to common allergens, according to a report published Monday in Pediatrics.
That doesn’t mean parents should be encouraging their children to start sucking their thumbs if they aren’t already doing it, says study coauthor Dr. Bob Hancox, an associate professor of preventive and social medicine at the Dunedin School of Medicine in New Zealand.
A safer strategy might be “having pets—cats and dogs—which also appear to protect against [allergies],” Hancox says. “Whether this is regarded as a positive behavior depends on family circumstances.”
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The findings do, however, provide more support for the “hygiene hypothesis,” which suggests the rise in the rates of allergic diseases in kids may be related to our obsession with providing a germ-free environment, Hancox adds.
When the environment is excessively sterile, the immune system can go wrong, experts say. It’s like having a large standing army with nothing to do. Those bored immune system soldiers will look for something to attack, and in some people, that means going after allergens.
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The new study followed 1,037 children born in 1972-1973 for more than three decades. Skin prick tests — in which small amounts of allergens are injected just underneath the skin — were done when the children were 13, and again when they were 32. When a person is sensitive to a particular substance, welts appear at the injection site.
At age 13, 38 percent of the children who bit their nails or sucked their thumbs showed sensitivity to allergens such as dust mites, grasses and dog dander, compared to 49 percent of the children who displayed neither habit. Just 31 percent of children with both habits showed sensitivity.
The link between allergen sensitivity and thumb sucking and nail biting was still seen at age 32.
Related: Feeding kids peanuts prevents allergies long-term, study shows
Still, the researchers did not find a connection between those habits and the likelihood a child would develop hay fever or asthma.
The new findings are “intriguing,” says Dr. Alison Morris, a professor of medicine in the division of pulmonary, allergy and critical care at the University of Pittsburgh and director of the university’s Center for Medicine and the Microbiome.
“If parents can’t get their kids to stop sucking their thumbs, this may make them feel better about that,” Morris says. “But I don’t think the study offers anything actionable at this point other than to be more relaxed about children’s exposures to germs.”