How long it takes for jaundice to become nuclear jaundice in babies is mainly related to the severity of the jaundice and the individual factors of the child, and there are individual differences in the exact duration. The jaundice in babies is bilirubin encephalopathy, mainly due to the more serious jaundice and high bilirubin levels in the body, which has little to do with the duration of jaundice. Nuclear jaundice mostly appears as a symptom 4-7 days after birth and is the most serious complication of neonatal hemolytic disease. If the jaundice is physiological or the value is low, there is usually no need to worry and symptomatic treatment is sufficient; if the jaundice is pathological and the value is high, the change in jaundice should be closely observed and timely treatment with blue light irradiation or medication should be administered to prevent nuclear jaundice from occurring. In addition, if the baby shows obvious yellowing of the skin and gradually develops symptoms of yellow body, yellow eyes, yellow urine, accompanied by fever, easy to panic and convulsions, etc., it is considered to be the early symptoms of nuclear jaundice, and early correction is recommended.