Common causes of newborn babies’ genitals shrinking inside include physiological causes, pediatric hernia and hidden penis. 1. Physiological reasons: the genitals of newborns are often small and not easily visible. Some newborns have genitals shrinking inside, but the phenomenon of normal urination, generally a normal physiological phenomenon, to be gradually developed and grown up genitals, can return to normal. 2. Pediatric hernia: When a newborn with a pediatric hernia cries, the abdominal pressure rises, and the contents of the hernia fall into the scrotum, increasing the volume of the scrotum, and when the foreskin is lifted, it looks like the genitals are shrunken inside. 3. Hidden penis: this is a kind of congenital developmental problem of newborns, because there are many abnormalities during the development of newborns’ genitals, such as abnormal development of the endothelium, formation of fibrous girdle and poor fixation of the root of the penis, resulting in obstacles to protrusion. If a newborn’s genitals are shrunken inside, it is important to take the baby to the hospital in time to seek medical treatment, and targeted treatment will be carried out after the cause is found out by a professional doctor.