Long-term thumb-sucking has never really been considered a good thing, particularly when it carries on well past the baby stage. After all, anyone who’s ever had a toddler knows that those adorable little hands of theirs are basically a treasure trove of germs, despite all your best efforts. Same goes for nail-biting, too, which most people tend to view as just downright gross.
But according to a recent study published in the journal Pediatrics, the “nasty” habits may actually have their advantages: Researchers have now linked thumb-sucking and nail-biting to lowering a child’s risk of developing certain allergies.
Turns out, all those yucky germs and microbes your kid is exposing themselves to by sticking their fingers in their mouth may actually help boost their immune system. In the process, they’re protecting themselves against allergens found in pets, grass, and dust mites.
At least, that’s the theory. Scientists are still sort of working through the details.
“How exactly exposure to microbes alters immune function in this way is not known,” said Bob Hancox, a co-author of the study and an associate professor at the University of Otago’s Dunedin School of Medicine. “But it is suggested that increasing microbial exposure influences the immune system to fighting infections rather than developing allergies.”
According to the CDC, some 50,000 Americans suffer from allergies each year, and food and skin allergies in kids have spiked over the last few decades. (We’ve seen this most predominantly with the rise of peanut allergies, for which scientists are still trying to find a cause.)
But all of this is precisely what drove the recent study. “Understanding why so many people have allergic disease is important,” Hancox told CNN in July.
During the study, New Zealand researchers followed the oral practices of more than 1,000 children from their births (in 1972 and 1973) to adulthood (making most about 32 or 33 now). At ages 5, 7, 9, and 11, their parents filled out questionnaires for the researchers, noting their thumb-sucking and nail-biting habits. According to study authors, 31% of the children involved in the study were frequent thumb-suckers or nail-biters.
Researchers administered two skin-prick tests over the course of the study to determine whether or not the children had allergies — one at age 13, and one at age 32. Turns out, frequent thumb-suckers and nail-biters had a 30-40% less chance of developing allergies in childhood that persisted into adulthood (though no associations could be found between the habits and asthma or hay fever specifically).
Of course, the study’s findings aren’t exactly a ringing endorsement of thumb-sucking or nail-biting. After all, there’s plenty of other research out there that’s found the habits could do everything from negatively affecting your teeth alignment to spreading warts (ick). But at the very least, maybe it’ll allow former (and current) nail-biters and thumb-suckers everywhere to cut themselves some slack for not kicking the habits sooner. There was some silver lining after all.