According to the American Academy of Pediatric Dentistry, the physical effects of prolonged thumbsucking are anterior overbite, increased overject, development of posterior crossbite and increased risk of trauma to maxillary incisors. Keep in mind, however, that this applies to prolonged use only. "Not all thumbsucking causes dental damage," says Dr. Rosemary M. Jackson, a pediatrician at the SUNY Downstate Medical Center in Brooklyn, N.Y.

According to the Journal of the American Dental Association, children who digit suck at age 4 or beyond run a greater risk of developing an overbite and alternating the way their jaws fit together. As your toddler begins to explore his world and not so sanitary things such as the dog's water dish or the toilet, his thumbsucking can give him a higher risk of infections.

Dr. Jackson says aggressive thumbsucking, or children who suck their thumb with great intensity and tongue thrust, are at a higher risk for infections, too. "Parents should look for calluses and fragile skin," she says. "Impetigo and fungus are two possible thumb infections." Consult your child's physician if he exhibits any unusual symptoms such as these.