Children in the study were reported by their parents as being thumb-suckers or nail-biters at ages 5, 7, 9 and 11.

These study participants were given skin-prick tests at ages 13 and 32 to detect allergies. These tests can reveal allergic reactions to 40 substances, according to the Mayo Clinic.

The results of the first skin-prick tests showed that 38 percent of children who were either thumb-suckers or nail-biters had allergies compared with 49 percent of children who had neither habit.

Furthermore, children who both sucked their thumbs and bit their nails had an even lower risk of allergies — 31 percent.

Researchers found that results of skin-prick tests remained consistent when the second test was given at age 32. Gender, parental history, pet ownership and other factors seemed to have altered the outcomes very little.