What is the cause of physiological jaundice in a breastfeeding newborn who becomes jaundiced three days after birth?

Physiological jaundice in a breastfeeding newborn typically arises due to the immature liver function that is common in newborns. After birth, the infant's liver is still developing and may not efficiently process bilirubin, a byproduct of the normal breakdown of red blood cells. This inefficiency can lead to elevated levels of bilirubin in the blood, which manifests as jaundice.

In the case of newborns, it's normal for bilirubin levels to rise during the first week of life as the newborn's body adjusts to extrauterine life. This process involves the liver gaining the ability to conjugate and excrete bilirubin more effectively over time. The peak of physiological jaundice usually occurs around the third to fifth day of life, aligning with the timing of jaundice onset observed in this scenario.

Other options might involve feeding issues or breastfeeding difficulties that can contribute to jaundice, but physiological jaundice itself stems directly from the inherent immaturity of liver function in newborns. This is a critical distinction that helps in understanding the normal transition of a newborn's capabilities and the management of jaundice.