A study in the journal Pediatrics, published by the American Academy of Pediatrics, has found that the common childhood habits of thumb sucking and nail biting can reduce the risk of adolescent and adult allergies.
Researchers followed more than 1,000 individuals from 5 through 32 years old, monitoring these two habits at ages 5, 7, 9 and 11. The subjects were tested for allergies at age 13 using a skin-prick test, and then tested again at age 32. Of all participants, 31 percent were frequent thumb suckers and nail biters, and those children had a lower incidence of allergic reactions than the others. These results support a hygiene hypothesis suggesting that early exposure to microbial organisms reduces the risk of developing allergies