Sucking is a baby's first instinct and it is healthy and normal for babies to suck their thumbs and fingers, as it is linked to their need for food and exploration. The desire varies greatly from one baby to another and while one baby may have little interest in their thumb, another may have it permanently positioned in their mouth.

Thumb sucking tends to decrease when a baby starts eating solid food, at around 6 months and the need to suck generally lessens or stops around 12 months. Thumb sucking or the use of a dummy by a baby is usually little cause for concern for dental development up to this age. Up to 90% of infants suck their thumb and fingers without any adverse effects, and most will stop between the ages of 2 and 4 years.

However, after the age of 2 years, thumb sucking can be a problem and around 30% of preschool children will continue. By this stage, a child will most likely continue to suck their thumbs out of habit but some may also continue because of boredom, fatigue, stress or worry.

The habit is best broken before the permanent teeth appear in the mouth. However if the habit persists after the permanent teeth start to appear, the thumb or fingers may force the teeth and jaw out of alignment. This problem may then need correction.