Jaundice in newborns is one of the most common reasons babies are kept in hospital after birth or readmitted in the first weeks of life. For parents, seeing their newborn under bright blue lights with an eye mask in place is distressing. Understanding what is happening, why, and what the treatment involves makes the experience significantly less frightening.
What Causes Newborn Jaundice?
Foetal red blood cells have a different structure from adult red blood cells and are broken down rapidly after birth. This breakdown produces bilirubin, a yellow pigment. The neonatal liver must process and clear this bilirubin, but in the first days of life the liver's processing capacity is limited. Bilirubin accumulates in the blood and deposits in the skin and whites of the eyes, causing the yellow colouring of jaundice.
This physiological jaundice affects up to 60 percent of full-term babies and 80 percent of premature babies. It typically appears on day 2 to 3, peaks around day 3 to 5, and resolves by day 10 to 14. For most babies it is mild and requires no treatment beyond ensuring adequate feeding to promote bilirubin clearance through the stool.
When Is Phototherapy Needed?
Phototherapy (bili lights or jaundice lights) is recommended when bilirubin levels reach specific thresholds that vary by gestational age and postnatal age. The thresholds are lower for premature babies because their blood-brain barrier is less mature and they are at higher risk of bilirubin reaching the brain (kernicterus — the serious complication that phototherapy prevents).
Your paediatrician uses a nomogram (threshold chart) that accounts for your baby's exact age in hours, gestational age, and risk factors to determine whether phototherapy is needed. Trust this assessment — the thresholds are evidence-based and the decision is made to prevent a rare but serious outcome.
What Phototherapy Involves
Your baby is placed under special blue-spectrum lights (not UV and not dangerous) with eye shields to protect their eyes. The light penetrates the skin and converts bilirubin in the blood into a water-soluble form that can be excreted without liver processing. The baby needs to be under the light as continuously as possible — time off the lights for feeding is fine, but other holding should be minimised during active treatment.
Frequent feeding is critical during phototherapy — breastfeed or give formula every 2 to 3 hours. Bilirubin is primarily cleared through the stool, and more feeding means more stools and faster bilirubin clearance. Water supplementation does not help bilirubin clearance and should not be given.
Warning Signs in Jaundiced Babies
Jaundice appearing in the first 24 hours of life is never physiological and requires immediate evaluation — see a doctor the same day. Jaundice extending below the belly button suggests higher bilirubin levels and needs urgent assessment. A baby with jaundice who is very sleepy, refusing feeds, has a high-pitched cry, or arches their back needs emergency evaluation for bilirubin encephalopathy.