A thumb-sucking child usually places the thumb in the mouth above the tongue, pressing forward against the upper front teeth or gums and backward against the lower front teeth or gums. A child may develop a callus on the thumb if he or she sucks often and very hard.

• Some children suck their fingers instead of their thumbs. They may have found their fingers more easily than their thumbs when they first started sucking.
• Some children finger a piece of cloth, pull on their ears, or twist their hair while sucking.

Thumb-sucking in children younger than 4 is not usually a problem behavior. Children who suck their thumbs frequently or with great intensity after the age of 4 or 5 may develop:

• Emotional difficulties. Some preschoolers who suck their thumbs may feel ashamed if they are teased by other children. Parents can cause low self-esteem by ridiculing or punishing their child for this behavior.
• Dental problems. Thumb-sucking can cause many serious future dental problems, such as improperly aligned teeth (malocclusion). Malocclusion usually corrects itself when the child stops thumb-sucking. However, the longer thumb-sucking continues, the more likely it is that orthodontic treatment will be needed to correct any resulting dental problems.
• Speech problems. The most common speech problems that develop because of thumb-sucking include mispronouncing Ts and Ds, lisping, and thrusting out the tongue when talking.