PhotoIf the inside of your child’s mouth frequently sees a nail or thumb, you may have logged your share of hours attempting to discourage this habit.

Apart from the fact that thumb-sucking can create dental problems, kids’ fingers can be a haven for all kinds of germs and bacteria. But, as it turns out, exposure to hand-dwelling bacteria in early childhood may offer a health advantage.

A new study published in the journal Pediatrics has found that thumb-sucking and nail biting habits may help kids develop better immune systems later in life.

Fewer allergies

Researchers found that children whose parents described them as thumb-suckers and nail-biters had better immune systems and were less likely to test positive for allergies at ages 13 and 32.

More than 1,000 kids in New Zealand took part in the ongoing study, which looked at children's habits at ages 5, 7, 9, and 11. At age 13, kids were tested for common allergies including dust mites, dogs, cats, and grass. The researchers checked in on participants again when they were 32 years old.

They found that those who sucked their thumb or bit their nails during childhood were less likely to have an allergy. The likelihood of developing an allergy was even more diminished if participants engaged in both behaviors during childhood.

Hygiene hypothesis

The study’s author, Robert J. Hancox, says these findings are in line with the pacifier study -- an earlier study in which researchers found that kids whose mothers cleaned their pacifiers by sucking them were less likely to develop allergies.

Both studies support the “hygiene hypothesis," which is the idea that immune response and risk of allergies may be influenced by exposure to germs and certain microbes during early childhood.

But while kids prone to putting their hands in their mouths were less likely to develop skin allergies, the study found no impact on the risk of developing hay fever or asthma.

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