A harmless childhood habit of sucking the thumb for comfort.

About half of all children suck their thumbs during infancy, with most starting in the first months of life. Ultrasound pictures of intrauterine life have even shown fetuses sucking their thumbs. Infants explore their world by putting objects in their mouths and sucking on them. Thumb sucking appears to be a natural habit of children in all parts of the world. Sucking the thumb is soothing for a small child, and many children continue this habit for comfort and security into the early school years. Thumb sucking is most prevalent in children under two, and most children give up the habit on their own by age four.

Thumb sucking by itself is not a cause or symptom of physical or psychological problems. It is not known why some children suck their thumbs longer than others. More...