Kids who suck their thumbs or bite their nails past preschool age may drive their parents crazy, but at least the habits appear to incur a health benefit: a reduced risk of allergies. So report researchers in a new study showing that the protective effect lasts into adulthood. Their findings add further credence to the "hygiene hypothesis," which suggests that early exposure to microbes can help strengthen a developing person's immune system, reports US News & World Report. And kids who both suck their thumbs and bite their nails seem to enjoy an even greater protective effect, reports Scientific American, which adds that a similar study in 2013 found that kids had a reduced risk of allergies if their parents sucked their pacifiers clean.
While Dr. Robert Hancox, the paper's senior author out of New Zealand, says the benefits aren't strong enough to encourage kids into these habits, he adds that it's "difficult to imagine" what else would explain the decreased susceptibility to allergies his team found when looking at 1,000 New Zealand children into adulthood. Meanwhile, a pediatrician who reviewed the study said that this doesn't mean kids should "roll around in the dirt," but that adults can "loosen up a little" about cleanliness. By the way, one in three of the kids studied were either sucking their thumbs or biting their nails "frequently" between the ages of 5 and 11 and enjoyed being a third less likely to develop allergic sensitization than their peers by age 13; those numbers held through the study's conclusion, when they were 32. (This woman is allergic to her own sweat and tears.)