Kernicterus (also called chronic bilirubin encephalopathy) is a very rare type of brain damage that occurs in a newborn with severe jaundice. It happens when a substance in the blood, called bilirubin, builds up to very high levels and spreads into brain tissues.

Kernicterus can cause long-term hearing loss, intellectual disability, and behavior problems.

Kernicterus may be prevented by treating jaundice that is not getting better when it should be.

Babies who are at risk for severe jaundice will have a transcutaneous bilirubin test and/or a blood test to check the blood bilirubin level. Doctors start treatment for babies whose bilirubin levels are higher than they should be. If bilirubin reaches a level where kernicterus is a concern, the baby may be given a blood transfusion.

Once symptoms of kernicterus are noticed, brain damage is already occurring. A baby with kernicterus is very sleepy and lethargic. A lethargic baby does not ever seem fully awake. He or she also does not eat well, does not respond to touching, or does not startle from sudden movements.

A baby with kernicterus usually also has a very high-pitched cry that does not sound normal. The baby has poor muscle tone. He or she may seem "floppy" and weak. Sometimes this floppiness will suddenly change to muscle stiffness and tension. During these periods, the baby may arch his or her back and head.

A fever that occurs along with these other symptoms is also a sign of kernicterus. A baby with signs of kernicterus needs emergency medical treatment to help prevent more brain damage.