How Thumb Sucking and Nail Biting Impact the Risk of Developing Allergies

    Friday, 08 July 2016 07:00  Blog

How Thumb Sucking and Nail Biting Impact the Risk of Developing AllergiesA new study has reported that children who suck their thumbs or bite their nails may be at a lower risk for developing allergies than those kids who keep their fingers out of their mouths. This finding is quite intuitive when you consider the hygiene hypothesis. According to the hypothesis, allergies have been occurring in higher frequency in recent decades because children are raised in cleaner environments than ever before. Because of their lack of exposure to germs, their immune systems do not learn to recognize innocuous environment material and therefore overreacts to it later in life, misinterpreting the material for something life threatening.

Those who support the hygiene hypothesis believe that other allergic diseases, such as asthma, eczema, and hay fever may all result from this increased environmental sterility early in life. However, this study did not find a relationship between thumb sucking or nail biting and these other allergic diseases. Nonetheless, other research has pointed to a role of allergens in staving off these allergic diseases. Specifically, research has shown that when parents suck babies’ pacifiers before putting them in their babies’ mouth, those babies develop asthma and eczema at a lower rate than those who do not do this “cleaning” practice. The idea behind this effect is that parents pass microbes from their adult mouths to their babies, thereby introducing substances to their systems that they would not otherwise experience at that age.

The specific results of this study were that kids who sucked their thumbs or bit their nails were less likely to test positive for certain allergies when they underwent skin prick tests. The study, which tracked 1000 people who were born in 1972 or 1973 over 3 decades, collected information on thumb sucking and nail biting habits when the children were 5, 7, 9, and 11 years of age. They conducted the skin prick allergy test when the kids were 13. Whereas 49% of kids who did not engage in either of the relevant habits tested positive in response to common allergens, only 38% of those who regularly put their fingers in their mouth tested positive. Of those who both sucked their thumbs and bit their nails, only 31% tested positive. The specific allergies that were tested included dog dander, cat dander, dust mites, and grass.

When these children grew up and were tested at age 32, the protective effect of thumb sucking and nail biting still appeared to be there. Though those who engaged in both habits did not experience allergies less frequently than those who engaged in just one, those who had sucked their thumb or bitten their nails were still less likely to test positive for allergies than those who had not done either. These effects held up even when researchers controlled for other variables such as gender, family history of allergies, owning a pet, parental smoking, and breastfeeding.

Though these findings fit nicely with the hygiene hypothesis, they do not prove that there is a causal relationship between thumb sucking or nail biting and allergies. Researchers therefore emphasize that it would be too hasty to start to recommend that children suck their thumbs or bite their nails as a way to protect against developing allergies. Instead, further research will help clarify the relationship between these habits and allergies specifically, and the potential role of early exposure to “germs” and other substances in allergy development.

 

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