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Thumb-Sucking, Nail-Biting Could Help Young Children Battle Common Allergies

NEW YORK (CBSNewYork) -- You probably heard it from your mother over and over again - stop biting your nails, and don't suck your thumb.

Those are two of the hardest habits for kids to break, but as CBS2's Dr. Max Gomez explained a new study found they could have health benefits.

For a long time doctors have tried to explain the significant increase they're seeing in children's allergies.

Things like asthma, hay fever, and eczema are on the rise.

One theory is that the environment kids are being raised in is too clean -- thumb-sucking and nail-biting changes that.

Like a lot of kids, Gracie Ingram used her hands to soothe herself as a baby.

"When I was little instead of sucking a pacifier I sucked my fingers instead," she said.

Like a lot of parents her dad Chris couldn't stop her.

"We felt like we ought to discourage it but she was pretty tenacious," he said.

It turned out Gracie may have been doing a good thing.

A new study published in the journal Pediatrics shows children who bite their nails and suck their thumbs are about one-third less likely to develop certain allergies.

"Cat, grass, house dust mite, and dog. Those were all reduced, some of them significantly, some borderline," Professor Malcolm Sears, McMaster University School of Medicine said.

Researchers said the findings are part of a growing body of evidence to support what's called the hygiene hypothesis -- the idea that being too clean may keep a child's immune system from developing normally.

"The theory goes that in the early environment, if we're not exposed to enough of these germs and other things that normally we consider bad things, then we won't be ready when we're challenged in the future. In this population that they're studying, often allergic families, they may be more likely to develop those allergic diseases and autoimmune diseases as a result," Dr. Clifford Basset, Asthma and Allergy Care of New York, said.

Thumb or finger sucking, as well as nail-biting exposes a child to germs and other antigens that might actually help the immune system mature appropriately.

It's not a habit without downsides. Pediatric dentists caution that kids who continue to suck their fingers risk problems with proper alignment of teeth. The alignment often corrects itself if it hasn't gone on beyond about age 4. It's a problem that can also occur with pacifiers.

One mother suggested letting kids be kids.

"You should be out playing in the grass and playing in the dirt right/ That's what kids should do," Salima Milliot said.

While researchers said that a little dirt on the fingers and nails may be a good things when it comes to reducing allergies, they also said it's not a reason to encourage your kids to suck their thumbs.

Parents shouldn't agonize over it however, as it is often a habit that begins in the womb.

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