Josh Kingsley, age 13, of Birmingham, Ala., for his question:

WHAT CAUSES JAUNDICE?

Jaundice is a yellowish discoloration of the skin, the tissues and the whites of the eyes. It results from an increased amount of bilirubin, a reddish yellow pigment in the blood.

Bilirubin is formed by the breakdown of hemoglobin, a pigment in red blood cells. The liver removes bilirubin from the blood stream and secretes it in the bile. Thus, jaundice results from either excessive production of bilirubin or reduced secretion of bile.

Jaundice is not a disease, but a symptom of various diseases.

Many babies are born with physiologic jaundice, which occurs if the body cannot process all the bilirubin it produces. In most cases, this condition disappears by the time the baby is two weeks old.

Hemolytic jaundice results from an increased breakdown of red blood cells which causes a greater concentration of bilirubin in the blood.

Hepatocellular jaundice occurs when the liver is damaged so that it cannot secrete enough bile.