Using light to induce a chemical reaction which reduces the level of the pigment bilirubin in the blood of newborn babies. A raised bilirubin causes the individual's skin to have a yellowish tinge – JAUNDICE. While this is a common and usually harmless finding in many newborn babies whose immature livers cannot handle the rapid breakdown of red blood cells after delivery (the source of the pigment), high levels of jaundice may occur in very premature babies and those with HAEMOLYTIC DISEASE OF THE NEWBORN, due to incompatibility between maternal and fetal BLOOD GROUPS. Such babies are at risk of brain damage from kernicterus (staining of the basal ganglia of the brain with bile pigments) which may result in hearing impairment and/or learning disability.

Consequently, in neonatal units, doctors and midwives keep an eye on jaundice levels, checking them where necessary by taking a blood sample. This allows them to intervene before potentially dangerous levels are reached. After referring to standardised charts, a baby may be placed under a light-emitting source, called a phototherapy unit, which will reduce the rate of rise of jaundice or cause it to fall. If this proves insufficient an exchange BLOOD TRANSFUSION may prove necessary. However, the overwhelming majority of babies who become jaundiced at birth come to no harm.