A group of scientists from New Zealand found that children who suck on their thumb and bite their nails are less likely to develop certain allergic reactions. Previous studies had already established a relationship between these two activities and an improved immune system, but a recent paper authored by Stephanie J. Lynch identifies specific benefits regarding atopic sensitization.
Scientists have known that a regulated exposure to bacteria strengthens the body’s immunological system. Like martial artists, little amounts of bacteria let the body “practice” and learn new ways to defend itself from certain kinds of problems. In the past, specialists had considered thumb sucking and nail biting as a natural mechanism of microbial exposure, but they were not sure what the effects on allergic diseases were.
To deepen into the subject, Dr. Lynch and her colleagues decided to analyze how these childish activities affect three distinct problems; atopic sensitization, asthma and hay fever.
Two bad habits are better than one!
1037 children from Dunedin participated in the Dunedin Multidisciplinary Health and Development Study, a cohort study that started back in 1972. The specialists used a questionnaire to identify how many of these kids sucked their thumbs and bit their nails. From the whole group, 31% of the children had one of these habits during their childhood, between 5 and 11 years old. 724 of the participants went through a skin-prick testing when they were 13 years old to detect atopic sensitization, and the team kept track of the medical history to identify asthma and hay fever supported by pre-made questionnaires.
The specialists followed the participants until their adulthood and found direct benefits in the case of allergic reactions. 724 of the 1037 children went through skin-prick testing, and 328 (45%) of them were diagnosed with atopic sensitization. According to the researchers, kids who had at least one of the studied habits were less likely to develop an allergy (38%).
Moreover, the ones that engaged in both thumb sucking and nail biting during their childhood had fewer chances of developing sensitization (31%). In contrast, the participants who did not engage in any of these activities were much more susceptible to the problem (49%). The benefits were very similar for both activities, and the results were not significantly affected by the gender.
How accurate are the results?
The skin-prick testing was applied to the participants when they were 13 years old. Their skin was exposed to different allergens to see whether there was a reaction. The items included house dust mite, grass, cat, dog, wool and so on. Then, the tests were repeated on 93% of the participants when they were 32 to analyze how long the protective effect lasted. The specialists concluded that children who suck their thumb and bite their nails are considerately less likely to develop atopic sensitization, and the protective effect lasts at least until they are 32.
However, the researchers could not prove that these two habits can prevent asthma or hay fever. The resulting study was published on-line in Pediatrics by the American Academy of Pediatrics on July 11, 2016.