A by-product of hemoglobin metabolism. Hemoglobin is found within red blood cells. As old, damaged or unneeded cells are cleared from the bloodstream, hemoglobin is broken down and several ‘waste products’ are formed, including bilirubin. Bilirubin is cleared by the liver. In the newborn, the immature liver often cannot clear bilirubin fast enough, and it builds up within the body, causing a yellow hue to the skin called jaundice. (This can also happen in the older individual when the burden of bilirubin becomes too great for the liver). Excess bilirubin can cause sleepiness and poor appetite in a baby, and when severe, can cause an irreversible brain damage called kernicteris, though this is rare. A small amount of jaundice is seen in most babies in the first week of life. Many nurseries now check the level of bilirubin before discharge.