Thumb suckers and nail biters less susceptible to allergies: study

"The bottom line is don't be afraid of a little dirt," says McMaster researcher Malcolm Sears.

'The bottom line is don't be afraid of a little dirt,' says McMaster researcher Malcolm Sears

New research shows that children who suck their thumbs or bite their nails are less likely to develop allergic sensitivities. (Shutterstock)

Can't stop your kid from sucking his or her thumb? Now there's less reason to fret about that. New research shows children who suck their thumbs or bite their nails are less likely to develop allergic sensitivities.

Malcolm Sears is a professor at McMaster University's DeGroote School of Medicine. (McMaster University)

The study from New Zealand's Dunedin School of Medicine was published Monday in the journal Pediatrics. Professor Malcolm Sears from McMaster University's DeGroote School of Medicine assisted.

Sears says he's not necessarily encouraging children to suck their thumbs. But there does appear to be a correlation between these habits and allergy to dust mites, grass, cats, dogs, horses and fungi.

It seems to contribute to the "hygiene theory" that early exposure to dirt or germs reduces the risk of developing allergies.

"The bottom line is don't be afraid of a little dirt," he said.

Researchers measured this by looking at more than 1,000 New Zealand children at ages five, seven, nine and 11. They also did skin-prick testing at 13 and 32 years.

Of those kids, 31 per cent were thumb suckers or nail biters. Researchers compared those who said they regularly indulged in these behaviours with those who said they didn't suck their thumbs or bite their nails at all.

The study found that among the 13-year-olds, 45 per cent showed they were more susceptible to allergies. But among the thumb suckers or nail biters, only 40 per cent had allergies. And among those who both sucked their thumbs and bit their nails, only 31 per cent had allergies. The trend continues into adulthood.

The study didn't find a correlation between those habits and asthma or hay fever. It also doesn't address how often the children indulged in those behaviours, or for how long, Sears said.