The survival of a newborn baby depends on instinctive nutritive sucking, which allows for essential nourishment. Infants also engage in nonnutritive sucking of their fingers and thumbs, which provides them with a sense of well-being, comfort, and security. Thumb sucking, however, can also have negative influences on both dental development and speech. The ultimate goal, however, should be to correct the cause of the habit, rather than the habit itself. The mouth provides a baby's first contact with the external world, and sucking is an infant's first coordinated muscular activity.
Babies even suck their thumb before they are born.
Prolonged thumb sucking can deform a child's upper dental arch, cause a crossbite, protrude teeth, and create an open bite. The extent of these negative consequences are affected by the duration of the habit, the daily frequency of the habit, and the manner in which the thumb is placed into the mouth. Children tend to suck their thumb when they are tired, bored, under stress, or in need of comfort. Taking away the soothing effects of a thumb habit may result in poor conduct by the child. Preventing a thumb habit, against the wishes of a child, may result in learning problems, bed wetting, sleep disorders, initiation of a new habit, or persistence of the old habit.