Health and Medicine

Thumb-Sucking and Nail-biting Children Less Likely to Develop Allergies in Adulthood

thumb sucking

A team of researchers from New Zealand’s Dunedin School of Medicine conducted a study to determine whether nail biting and thumb sucking have a positive effect in that these ‘bad’ habits do in fact prevent allergies. At the same time, the team investigated possible links between these habits and the development of hay fever or asthma.

In medical circles, the hygiene hypothesis states that if children are not exposed to germs and dirt early on, it could increase their risk of developing allergies, also known as atopic sensitization.

The research spans a period of a number of decades with it starting with children at age 5 and the final skin-prick testing done at 32 years old. The longitudinal birth cohort consisted of more than 1,000 children born in Dunedin, New Zealand in 1972-1973. The habits were measured at ages of 5, 7, 9 and 11, while the skin-prick testing to measure atopic sensitization was performed at ages 13 and 32.

In tests conducted on all 13 year olds, show that 45% have atopic sensitization. When children having either one of the habits were tested, only 40% of them had allergies. This reduces further to 31% for children having both habits. Malcolm Sears of McMaster University, one of the researchers notes that the trend continues into adulthood and is not dependent on external factors such as exposure to house dust mites, smoking in the household, or ownership of cats or dogs.

No associations were found between the oral habits and the development of hay fever or asthma. However, a wide range of allergies was found to be reduced, including to such things as airborne fungi, cats, dogs, dust mites and grass was found to be reduced.

Sears concludes that while these habits should not be encouraged as such, there is definitely a positive side to both nail biting and thumb sucking.

The research was published in the journal Pediatrics.