Nail biting and thumb-sucking in childhool could be a good thing. As ABC News reports on research touting the benefits of habits thought to be bad ones:

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.

It concludes:

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