Breast milk jaundice refers to idiopathic jaundice associated with breastfeeding, one of the common causes of neonatal jaundice. In addition to jaundice (yellow and bright skin color), the infant is completely healthy, sucks milk well, has normal bowel movements, and has satisfactory body mass growth. The etiology and pathogenesis are still unclear, but may be related to the increased activity of glucuronidase, an enzyme that is mainly derived from breast milk in the neonatal period, and the decomposition of direct bilirubin in the intestine into glucuronide and indirect bilirubin under the action of β-GD, which is absorbed by the intestinal mucosa into the enterohepatic circulation, resulting in an increase in unconjugated bilirubin in the serum and causing jaundice. It is the leading cause of jaundice in newborns. The main clinical feature is the appearance of jaundice soon after breastfeeding in newborns, but without other systemic symptoms, which is more common in full-term infants. With the increase of breastfeeding rate, the incidence of breast milk jaundice has increased year by year, and now it has reached 20%-30%, and has become one of the main causes of hyperbilirubinemia in hospitalized newborns. Recent data show that breast milk jaundice accounts for more than 50% of hyperbilirubinemia in hospitalized full-term infants. Although the prognosis of this disease is good and treatment is required only for severe cases, attention should be paid to the successful promotion of breastfeeding. Breast milk jaundice is generally classified into early and late onset. True breast milk jaundice refers to late onset jaundice, while early onset jaundice is also known as breastfeeding jaundice. Early-onset jaundice is similar to the time of appearance and peak value of physiological jaundice in newborns, i.e., it appears 2 to 3 d after birth and is most pronounced on the 4th to 6th day, and then subsides within 2 weeks. However, in clinical practice, the highest value of breast milk jaundice exceeds that of physiologic jaundice. Late jaundice often occurs in conjunction with physiologic jaundice and can be aggravated after the reduction of physiologic jaundice. The child is completely healthy except for jaundice (yellow and bright skin color), eats milk well, urinates normally, gains weight satisfactorily, and rapidly decreases bilirubin by about 50% 24 to 72 h after stopping breast milk. Phototherapy is a simple and effective method to reduce serum unconjugated bilirubin. The principle is that unconjugated bilirubin is converted into water-soluble isomers by the action of light and excreted through bile and urine. Since phototherapy only works on superficial skin tissues, the disappearance of skin jaundice does not indicate normal serum unconjugated bilirubin.