Why do newborn babies get jaundice, and when does it matter?
Because a newborn produces bilirubin faster than an immature liver can clear it, and the excess colours the skin and eyes yellow. Most jaundice is normal and resolves without treatment — but a small proportion is not, and the distinguishing features are mainly about timing.
Why it happens. Babies are born with a high red blood cell count, which breaks down rapidly after birth, releasing bilirubin. The newborn liver takes days to become efficient at processing it, and meanwhile the pigment accumulates. Roughly six in ten term babies and a higher proportion of preterm babies become visibly jaundiced.
The timing is what distinguishes normal from concerning:
Appearing in the first 24 hours is always treated as urgent, because the likely causes — including blood group incompatibility — are not the benign ones.
Appearing after day two or three, peaking around days three to five, then fading, is the typical benign pattern.
Persisting beyond about two weeks (three in preterm babies) needs investigating, because prolonged jaundice can indicate liver or biliary disease, and one condition in particular has outcomes that depend heavily on being treated early.
Pale chalky stools and dark urine alongside prolonged jaundice are the specific red flag, and are worth knowing about precisely because they are easy to dismiss.
Breastfeeding and jaundice. Jaundice is more common in breastfed babies and this is usually not a reason to stop. Feeding frequently helps clearance. Where poor feeding and dehydration are contributing, the answer is feeding support, not stopping.
Treatment. Bilirubin is measured — visual assessment is unreliable, especially on darker skin, which is a known source of missed cases — and plotted against age-specific thresholds. Phototherapy converts bilirubin into a form that can be excreted. Exchange transfusion is reserved for severe cases.
Why thresholds matter: very high levels can cause permanent neurological damage, which is entirely preventable with timely treatment.
General information, not medical advice.