Thumb sucking and nail biting may not be gross habits after all

“Our findings are consistent with the hygiene theory that early exposure to dirt or germs reduces the risk of developing allergies,” Sears said in a press release. The study comes out of New Zealand’s Dunedin School of Medicine and looked at 1,037 kids born between 1972 and 1973. In the early years, parents were asked to rate whether their children were frequent thumb suckers or nail biters.