More than half of all newborns develop some amount of jaundice, a yellow coloring in their skin, during the first week. This is usually a temporary condition, but it may be a sign of a more serious illness.
Jaundice is caused by the breakdown of red blood cells. As the old cells are broken down, hemoglobin is changed into bilirubin and removed by the liver. The buildup of bilirubin in the blood is called hyperbilirubinemia. Because bilirubin has a pigment, or coloring, it causes a yellowing of the baby's skin and tissues.
As liver function matures, the jaundice goes away. A premature infant is more likely to develop jaundice. The yellow tint to the skin can often be seen by gently pressing on the baby's forehead or chest and watching the color return.