What causes a baby to have jaundice?

Work backs up . Before delivery mom's body extracts all waste products from baby & allows babies organs to grow & function at minimal levels. At birth, the work switches to baby who must process & recycle hemoglobin from fetus blood so it can be used in regular blood.If there is extra bruising at delivery or a blood incompatibility, there is more work to do. The backup produces the jaundice.
Newborn jaundice. In order for a baby to exist in uterine, he has a special red blood cell. When born, those rbcs are destroyed. The waste product formed is excreted through the liver. Baby's livers are immature and they can't handle the great amount of waste product. Like a stuffed up sink the waste product backs up and causes jaundice. This is only a transitional situation.