Bilirubin is one of the products that is formed when red blood cells are broken down. Bilirubin is taken up by the liver and changed by an enzyme (protein that speeds up chemical reactions in the body) in the liver. It is then excreted through urine or stool. In newborn infants, this enzyme may work slowly or may not be present in large enough quantities to help remove bilirubin efficiently. This often causes jaundice, a yellowing of the skin and whites of the eyes, and is usually considered a physiologic (normal) jaundice that does not need to be treated. If infants have certain risk factors or become dehydrated because they are not drinking enough breast milk or formula, they might not be able to excrete bilirubin. This can lead to abnormally increased levels of the unchanged bilirubin in newborn infants' blood, a condition called neonatal hyperbilirubinemia.