What exactly is the phenomenon of jaundice in newborns? It starts with the characteristics of the newborn’s bilirubin metabolism. Since jaundice is caused by elevated bilirubin in the blood, there must obviously be some reason for the elevated bilirubin levels in the blood of newborns, mainly including a relative excess of bilirubin production and the poor ability of liver cells to process bilirubin. The daily bilirubin production in newborns is 8.8 mg/kg of body weight, while in adults it is only 3.8 mg/kg of body weight, and the ability of the liver cells to process bilirubin in newborns is also much worse than in adults. Although it is the responsibility of the pediatrician to identify whether neonatal jaundice is physiological or pathological and whether treatment is needed, it is not difficult to determine physiological jaundice and parents should have a general idea. The following characteristics of physiologic jaundice should be kept in mind by mothers and fathers of newborns: generally good; in full-term babies (gestational age between 259 and 293 days), jaundice appears only 2 to 3 days after birth, peaks in 4 to 5 days, subsides in 5 to 7 days, and does not exceed 14 days at the latest; in preterm babies (gestational age <259 days), jaundice appears mostly 3 to 5 days after birth, peaks in 5 to 7 days, and subsides in 7 to 9 days. Of course, the need for standardized treatment (such as phototherapy intervention) requires dynamic measurement of serum bilirubin values, combined with the presence of high-risk factors to assess and determine whether such bilirubin levels are normal or safe, simply put, the more high-risk factors, the greater the chances of jaundice causing bilirubin encephalopathy. There is usually no need to worry too much, but if there is neonatal hemolysis, asphyxia, hypoxia, hyperthermia, hypothermia, hypoglycemia, etc., you need to pay high attention. In addition to most cases of physiological jaundice, the rest of the cases require early and active treatment, otherwise a series of problems can be caused, and in severe cases can lead to bilirubin encephalopathy, resulting in irreversible damage to the nervous system and even death. Therefore, when parents find that jaundice appears within 24 hours after birth and lasts for a long time (>2 weeks in term babies and >4 weeks in preterm babies), it should never be taken lightly. There are many factors that can cause pathological jaundice including congenital genetic and metabolic factors, congenital malformations (biliary atresia), infections, hemolysis, etc. In cases such as biliary atresia in newborns, early diagnosis and intervention is very important, and surgery within 60 hours of birth is more effective, while delayed surgery can cause irreversible liver damage, and in some cases, liver transplantation is the only way to go if drainage fails. However, for well-known reasons, most parents in China choose to forgo treatment for this condition. Among the many pathological jaundices, there is one that deserves a special mention, and that is jaundice related to breastfeeding. This can be divided into two cases: the first is breastfeeding-related jaundice, where serum bilirubin rises due to inadequate breast milk intake and delayed defecation within a week after birth, a condition that can be experienced by almost two-thirds of breastfed newborns and can usually be relieved by increasing the amount and frequency of breastfeeding; the second is breastfeeding jaundice, which refers to jaundice in breastfed babies even after 3 months of life. This diagnosis is usually established only after the doctor has ruled out other conditions, and the jaundice can be significantly reduced by stopping breastfeeding for 48 to 72 hours. During the diagnosis and treatment of breast milk jaundice, we should be fully aware of its high incidence, not only in China, but also in the United States, where the re-hospitalization rate of newborns with jaundice in California was 6% higher in 2000 than in 1991. Medical professionals need not overly equate it with disease, as otherwise the majority of healthy hyperbilirubinemic children will be unnecessarily over-treated and over-labelled, increasing parental fear and wasting hospital resources. With the exception of rare case reports, most studies suggest that this type of jaundice has little impact on the long-term intelligence of the child. For jaundice that requires treatment, the most commonly used and effective modality is phototherapy (blue light is commonly used, but white or green light is also available, although I have not seen any hospitals mixing these types of light, so I guess it would have to be called a cocktail of phototherapy), but for non-pathological jaundice, blue light exposure is likely to do more harm than good, because recent studies have shown that elevated bilirubin in the neonatal period is part of the body’s stress response. Therefore, in critical cases, the question of whether or not blue light should be given is a matter of careful weighing between the toxicity of bilirubin and the benefits it brings to the organism.