The peak of jaundice in newborns is related to whether they are full term or not. Clinically most babies, whether full-term or premature, will develop physiological jaundice after birth, which is normal. The baby is in a state of relative hypoxia in the womb and the organism will maintain normal growth by increasing the number of red blood cells to carry enough oxygen. After birth, the child can get enough oxygen by breathing, so the excess red blood cells in the organism will be destroyed, and the destruction of red blood cells will release bilirubin, which will cause neonatal jaundice. For full-term newborns, jaundice usually peaks 4-5 days after birth, while in preterm infants, jaundice appears and subsides a little later than in full-term infants, usually peaking 5-7 days after birth. The appearance of jaundice in newborns must be taken seriously, and if necessary, blue light irradiation treatment should be given under the guidance of a medical professional to reduce the yellowing.