Rib ectropion is an abnormality in the appearance of the thorax, most often seen in normal infants and young children, and is due to the way they breathe. Rib flaring is a condition in which the lower ribs of the thorax protrude outward above the normal rib cage when an infant or young child is lying flat on their back, and to a lesser extent in adults. In infants and young children, abdominal breathing is usually the mainstay of breathing, and the abdominal cavity rises and falls during breathing. When inhaling, the pressure inside the abdominal cavity increases, which will lead to the protrusion of the ribs at the lower edge of the thorax. At the same time, the immature development of abdominal muscles in infants and young children can not effectively pull the rib edge, which in turn leads to the formation of rib ectropion. It should be noted that a small number of patients have congenital rib deformity, which is not a normal condition of rib ectropion. Overall, rib ectropion is a normal phenomenon that will gradually return to normal with age and does not require treatment.