Bilirubin

Bilirubin, a brownish-yellow breakdown product of red blood cells, can build up in the bloodstream. High levels can make the skin and whites of the eyes appear yellow, a condition called jaundice. Phototherapy converts the bilirubin to a form that can be processed by the liver and excreted.

Physiological Jaundice

Physiological jaundice, a mild condition, can occur when a baby's liver cannot work quickly enough to break down accumulated bilirubin. It generally appears two to four days after birth and disappears in about two weeks without phototherapy.

Jaundice in Premature Babies

Jaundice of prematurity may affect premature babies with even less developed livers. By speeding bilirubin elimination, phototherapy can prevent complications like deafness, cerebral palsy and other forms of brain damage.

Other Types of Jaundice

Jaundice can also occur when a baby doesn't get enough breast milk because of difficulty feeding and becomes dehydrated, or because the milk contains substances that raise bilirubin levels.

Effect of Phototherapy

Phototherapy alone does not address types of jaundice that result from problems like blood group incompatibility between the baby and mother. A doctor may combine light therapy with other treatments, depending on the type of jaundice affecting the baby.

Source:

Kidshealth.org: Jaundice in Healthy Newborns

Babiestoday.com: Phototherapy for Jaundice