thumbsucking, the habit of sucking the thumb for oral gratification. It is normal in infants and young children as a pleasure-seeking or comforting device, especially when the child is hungry or tired. The habit reaches its peak when the child is between 18 and 20 months of age, and it normally disappears as the child develops and matures. Thumbsucking beyond 4 to 6 years of age may lead to malocclusion of the teeth and deformation of the bony tissue of the thumb. Excessive thumbsucking, especially in older children, may be indicative of some emotional problem.
