2 “Bad” Habits That Could Prevent Allergies

By Katharine Paljug @kpaljug
October 03, 2016

Oral habits in children could have an unexpected benefit.

If you’re frustrated by your child’s thumb sucking or nail biting habit, you can breathe a sigh of relief. There could be a benefit to all those fingers in your child’s mouth.

According to a study published in the journal American Academy of Pediatrics, these two “bad” habits could prevent your child from developing allergies as they get older. 

The study was designed to test part of the “hygiene hypothesis,” which states that being exposed to a variety of microbial organisms in early childhood helps prevent children from developing sensitivities like allergies or asthma. The idea behind the hypothesis is that when children are exposed to bacteria and other microbes from a young age, the immune system is trained to attack these “invaders” rather than attacking itself, which is what happens in someone with allergies, asthma, or eczema. 




Allergies and asthma in children

Concern about these allergic conditions is growing as more and more children develop them in seemingly healthy Western countries. The Centers for Disease Control and Prevention report that in 2014 8.4 percent of children in the United States suffered from hay fever, while another 10 percent have respiratory allergies and 11.6 percent have skin allergies. That adds up to about 22 million children in the United States with allergic sensitivities, not including those with food allergies.

Asthma affects 8.6 percent of children under the age of 18, with the largest percentage of those between the ages of 5 and 14. Like allergies, asthma can vary in severity. Some children outgrow their allergies and asthma as they get older, but, for others, these can be life-threatening conditions that require constant management. 

Nail biting, thumb sucking, and “protection” from allergies

Children who bite their nails or suck their thumbs introduce many kinds of bacteria and germs into their mouths, potentially preventing them from developing dangerous allergic conditions.

Researchers in New Zealand tested the hypothesis that these two oral habits would lead to lower incidence of allergies, asthma, and hay fever by following more than 1,000 participants who were born between 1972 and 1973 until their 38th birthdays. At ages 5, 7, 9, and 11 years, the children’s parents reported their thumb-sucking and nail-biting habits. 


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At ages 13, 32, and 38, the participants were tested for allergies and other sensitivities using a skin prick test. They were also given respiratory tests to assess whether or not they suffered from asthma and were asked about experiencing hay fever. The results were then adjusted for factors like socioeconomic status, breastfeeding, pet ownership, and parents with allergic conditions. 

Researchers found that neither habit correlated to lower levels of either asthma or hay fever. However, both nail biting and thumb sucking were strongly related to whether or not participants developed allergies.

The study found that 31 percent of participants bit their nails or sucked on their thumbs at one or more of the ages observed, and this did seem to provide them some amount of “protection” against allergies. At age 13, 38 percent of children with an oral habit had an allergy, compared to 49 percent of children who neither bit their nails nor sucked their thumbs. 

The results were even stronger for children who had both habits: only 31 percent of them showed some kind of allergic sensitivity.

There are still downsides to both thumb sucking and nail biting habits. Though most children only suck their thumbs when they are very young, the American Dental Academy warns that children who suck on their fingers past the age of four may have problems with tooth alignment. Nail biting can put children at risk for skin infections if they bite their nails too short or chew on the skin around the nail.

However, if your infant or toddler has a tendency to put their fingers in their mouth for comfort, don’t worry too much. In the long run, they might just be healthier because of it. 


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October 03, 2016

Reviewed By:

Janet O’Dell, RN

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