Thumb-Suckers Develop Less Allergies

by Julia Newman (’19)

Fig. 1: Thumb-sucking in children may be related to later allergy development.

According to the popular Hygiene Hypothesis, if a child is exposed to bacteria and other microbes early in life, he will be more resistant to various bacterial illnesses. In order to test this premise, Stephanie Lynch of the American Board of Pediatrics and Malcolm Sears of the Department of Respirology at McMaster University conducted a study on thumb-sucking and nail-biting in children. The researchers hypothesized that the children who performed these actions would be less likely to develop allergies as they got older.

Using reports from parents about their child’s habits, Lynch and Sears found that on average, about thirty percent of children suck their thumbs, bite their nails, or do both. The researchers then performed skin-prick tests on each subject at ages thirteen and thirty-two, to see the child’s atopic sensitization, a predisposition toward allergy development. The results showed that the thumb-suckers and nail-biters overall showed eleven percent less sensitization than children who were not thumb-suckers and nail-biters. Also, the study found that the children who did both had an additional nine percent less sensitization when compared to children who only either sucked their thumbs or bit their nails.

This is clearly another set of results in a long list that supports the original Hygiene Hypothesis. Thus, studying the effects of these childhood habits on other diseases such as cancer may be the next step in what could become a revolutionary field of medicine.



  1. Lynch, M. Sears, Thumb-sucking, nail-biting, and atopic sensitization, asthma, and hay fever. American Academy of Pediatrics 138.2, (2016).
  2. Photo retrieved from:

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