Newborn jaundice happens when a baby has too much bilirubin in the blood, which makes the skin and eyes look yellow.

What is bilirubin?

  • Bilirubin is a yellow pigment made when red blood cells break down.
  • The liver normally processes bilirubin so it can leave the body in the baby’s poo.
  • If there is too much bilirubin, or the liver is still immature and cannot clear it fast enough, it builds up and causes jaundice.

The most common cause (normal “physiologic” jaundice)

In the first days after birth, many babies develop “physiologic jaundice,” which is usually mild and temporary.

Main reasons:

  • Newborns have more red blood cells than adults, so there is more bilirubin to clear.
  • Their livers are still maturing and are slower at processing bilirubin.
  • They may not be feeding a lot yet, so they poo less, which means less bilirubin leaves the body.

Other common causes and risk factors

These are still relatively common and often treatable:

  • Premature birth (baby born before 37 weeks): liver is even less mature and feeding can be harder.
  • Poor feeding or dehydration (for example, early breastfeeding difficulties): fewer wet/dirty nappies, so bilirubin doesn’t get cleared well.
  • Significant bruising or bleeding under the scalp from birth (cephalohematoma): extra red blood cells break down, raising bilirubin.
  • Blood type incompatibility between mother and baby (Rh or ABO problems): the baby’s red blood cells are destroyed faster, releasing more bilirubin.

Less common but more serious causes

These are rarer but important because they may need urgent treatment:

  • Infections in the blood (sepsis) or other serious infections present at birth.
  • Liver problems or blocked bile ducts (for example, biliary atresia) that stop bilirubin from leaving the liver.
  • Inherited enzyme problems (like G6PD deficiency or Crigler–Najjar syndrome) that affect how bilirubin is processed or how red cells survive.
  • Endocrine issues such as an underactive thyroid (congenital hypothyroidism).
  • Blood diseases that make red blood cells break down faster (certain anemias or abnormal red cell shapes).

What parents should watch for (story-style example)

Imagine a full-term baby who seems fine at birth. On day 3, the parents notice the baby’s face and chest are a bit yellow, but the baby is feeding well and has several wet nappies a day. The midwife checks the bilirubin level, says it is in the safe range for age, and the jaundice fades over the next week as feeding improves and the liver matures. This is typical “physiologic” jaundice.

Now imagine another baby whose yellow colour gets darker, spreads to the legs, and the baby is very sleepy, feeds poorly, or has pale or white stools and dark urine. That picture can suggest more serious jaundice or liver/bile duct problems, and doctors would test bilirubin levels quickly and investigate further.

When to seek urgent medical help

Contact a doctor or emergency service urgently if:

  1. Your newborn looks very yellow in the first 24 hours after birth.
  1. The yellow colour is getting worse instead of better.
  1. Your baby is very hard to wake, feeds poorly, or has a high-pitched cry.
  1. The stools are pale/white or the urine is very dark.

Severe untreated jaundice can, in rare cases, damage the brain (kernicterus), which is why early checking and treatment matter.

Quick list: what causes jaundice in newborns?

  • Normal newborn adaptation (physiologic jaundice, immature liver).
  • Prematurity.
  • Feeding difficulties and dehydration, including breastfeeding jaundice.
  • Bruising or internal bleeding from birth.
  • Blood group incompatibility (Rh or ABO problems).
  • Infections (sepsis and other congenital infections).
  • Liver diseases or blocked bile ducts (biliary atresia and others).
  • Genetic or enzyme conditions (G6PD deficiency, Crigler–Najjar, other red cell disorders).
  • Hormone problems like an underactive thyroid.

Information gathered from public forums or data available on the internet and portrayed here.

If this is about a specific baby (yours or someone you know), it’s important to have them seen directly by a pediatrician or emergency service so bilirubin levels can be checked and treated if needed.