How can high bilirubin levels cause kernicterus in newborns?

Kernicterus is a severe form of brain damage that occurs when high levels of unconjugated bilirubin accumulate in the blood and cross into the brain tissues of a newborn.12

Under normal conditions, bilirubin is transported in the blood bound to the protein albumin, which prevents it from entering the brain. However, when the rate of red blood cell destruction exceeds the liver's ability to metabolize and excrete bilirubin, the concentration of unconjugated bilirubin in the blood rises significantly. In extreme cases, this excess bilirubin can cross the blood-brain barrier and deposit in the brain, specifically targeting and destroying vital nuclei in the brain stem.3421

This condition is most frequently associated with erythroblastosis fetalis or prematurity, where metabolic systems are not yet fully developed. If left untreated, the resulting nerve-cell damage can lead to permanent disabilities, including cerebral palsy and hearing loss. Fortunately, this damage can often be prevented through medical interventions such as phototherapy or exchange transfusions.123