By John Kerr 12/07/2016

Children who engage in thumb-sucking and nail-biting are more likely to grow up to be free of some allergies, according to new research from the long-running Dunedin Study.

The world-famous study has followed a cohort of over a thousand children born in Dunedin in the early 1970’s, allowing unprecedented insights into what makes us into who we are (and is currently the subject of TVNZ documentary series Why am I?).

Way back in the 70’s and 80’s the children’s thumb-sucking and nail-biting tendencies were measured at ages 5, 7, 9 and 11. Later, at ages 13 and 32, their sensitivity to airborne allergens was measured by skin-prick testing.

The researchers found that among all children at 13 years old, 45 per cent showed a reaction to allergens in a skin prick test, but among those with one oral habit, only 40 per cent had allergies. Among those with both habits, only 31 per cent had allergies. Even two decades on, the authors find this trend carries on into adulthood; similar percentages were seen in the study members at age 32.

However the link wasn’t found for all allergies; the study did not find associations between the oral habits and development of asthma or hay fever.

The results, published in journal Pediatrics, offer strong support for the ‘hygiene hypothesis‘. This theory, first outlined in 1989 , posits that exposure to microbes when when young helps to build a strong immune system and reduces the risk of developing allergies.

You can read more about the research on

So is it a ‘good thing?’

Before you start putting up posters promoting thumb-sucking and nail-biting among youngsters it is important to note that there are other side effects to these oft-maligned behaviours.

Thumbsucking malocclusion
Thumbsucking malocclusion. NZAO

According to the New Zealand Association of Orthodontists, it is well documented that if thumb-sucking continues past the age of 5 to 6 years, “there is the potential for undesirable tooth movement and malocclusions may develop.”

Similarly, NZ dermatology website DermNet warns that thumb-sucking and nail biting can lead to Paronychia – infection and inflammation of the skin around fingernails.

These risks were not lost on the authors of the new study who also acknowledge the potential for other health problems to arise with fingers-in-mouths habits, concluding in their article:

…we do not suggest that children should be encouraged to take up these oral habits…

Featured image: Flickr / Packwood / Shand