Why it happens

Toddlers suck their thumbs because it's comforting and calming. Your toddler probably practiced this habit while he was still in the womb and perfected it as an infant. Now he may turn to his thumb when he's tired, scared, bored, sick, or trying to adjust to challenges such as starting preschool or going on a long car ride. He may also use his thumb to fall asleep at bedtime and to lull himself back to sleep when he wakes up in the middle of the night.

What to do about it

• Don't worry. Most children can safely suck their thumb — without damaging the alignment of their teeth or jaws — until their permanent teeth begin to appear. (Permanent teeth don't usually erupt until around age 6.) Also, not all children's thumb-sucking is equally damaging. Experts say it's the intensity of the sucking and the tongue's thrust that deforms teeth and makes braces necessary later. Children who rest their thumb passively in their mouth are less likely to have difficulty than children who suck aggressively. Watch your child and analyze his technique. If he sucks vigorously, you may want to begin curbing his habit earlier, say at age 4.

If your child's thumb becomes red and chapped from sucking, you can try applying a moisturizing ointment, cream, or lotion while he's sleeping. (If you apply it while he's awake, it may just end up in his mouth.).

• Let it go. Nagging or punishing your child won't help, because he doesn't usually realize when he's sucking away. Besides, pressuring him to stop may intensify his desire to do it even more. And techniques such as putting an elastic bandage on his thumb will seem like unjust punishment, especially since he indulges in the habit for comfort and security. Try to wait it out. Children usually give up thumb-sucking when they've found other ways to calm and comfort themselves, says pediatrician Suzanne Dixon. For example, while a toddler who's hungry may suck his thumb, an older child (age 3 or 4) might simply open the refrigerator and look for something to eat or ask his parents for a snack instead.

• Preempt the thumb-sucking with other activities. If you can identify times and places when your child is particularly likely to suck his thumb — while watching television, for example — you might try giving him a substitute, such as a rubber ball to bounce or puppets to play with. If he tends to suck his thumb when he's tired, work more naps into his schedule. Or if he turns to it when he's frustrated, help him put his feelings into words. The key is to notice when and where sucking occurs, and divert his attention by offering an alternative.