Jaundice — the yellow discolouration of the skin and whites of the eyes — is one of the most common conditions encountered in newborns in the first week of life. For most families, it is a visible but transient feature of the normal newborn period; for some, it requires treatment. Understanding why jaundice occurs, what the normal pattern looks like, and which features require urgent attention helps parents and carers identify when to seek advice without unnecessary alarm about a very common condition.
Healthbooq supports parents through the newborn period with evidence-based guidance on the common conditions of the first days and weeks of life.
Why Jaundice Occurs
Bilirubin is a yellow pigment produced when red blood cells break down. In adults and older children, the liver processes bilirubin efficiently and excretes it. In newborns, several factors combine to produce elevated bilirubin levels: the fetal circulation uses a different type of haemoglobin (fetal haemoglobin), which breaks down rapidly after birth; newborns have a higher red blood cell count than adults; and the newborn liver's capacity to process bilirubin is immature, particularly in the first days of life.
This physiological jaundice is normal and expected in the context of the transition from fetal to neonatal circulation. It typically appears on day two to three of life, peaks on day four to five, and resolves by the end of the second week in term babies. It is not a sign of illness.
Physiological Versus Pathological Jaundice
The distinction between physiological (normal) and pathological (requiring investigation and potentially treatment) jaundice rests on timing, severity, and course. Jaundice appearing in the first twenty-four hours of life is never physiological and requires urgent assessment — it suggests a pathological cause such as haemolytic disease (where the mother's antibodies cross the placenta and destroy the baby's red blood cells, as in Rhesus incompatibility or ABO incompatibility) or congenital infection.
Jaundice that is unusually severe (very yellow, involving the palms of the hands and soles of the feet, which do not yellow in physiological jaundice), that appears to be progressing rather than improving after day five, or that persists beyond fourteen days in a term baby (twenty-one days in breastfed babies or preterm babies) requires assessment. Prolonged jaundice in a breastfed baby is usually benign (breastmilk jaundice), but persistent jaundice beyond two weeks requires review to exclude liver disease, including biliary atresia — a rare but serious condition in which the bile ducts are absent or blocked.
Measuring Bilirubin
In the UK, jaundice in newborns is assessed by measuring bilirubin levels — either by a transcutaneous bilirubinometer (a device placed on the skin) or by a blood test (serum bilirubin). The decision to treat is based on the bilirubin level relative to the baby's age in hours and their gestational age, using standard threshold charts (NICE guidelines). Treatment is not based on the degree of yellowness perceived visually.
Phototherapy
The primary treatment for neonatal jaundice is phototherapy — exposure to specific wavelengths of light (usually blue-green light) that convert bilirubin in the skin into a water-soluble form that can be excreted in urine and stool without liver processing. The baby is placed unclothed (except for eye protection) under the phototherapy lamp, with feeding continuing normally. Breastfeeding should not be discontinued during phototherapy; adequate milk intake supports bilirubin clearance through stool.
Phototherapy is very effective and is usually sufficient. Exchange transfusion — replacing the baby's blood — is reserved for very high bilirubin levels not responding to phototherapy.
Kernicterus
Severely elevated bilirubin can cross the blood-brain barrier and damage the brain — a condition called kernicterus. Kernicterus causes a characteristic pattern of brain injury including hearing loss, movement disorder (athetoid cerebral palsy), and damage to eye movement. It is rare in the modern era of systematic bilirubin monitoring and phototherapy, but remains a concern in contexts where jaundice is not adequately assessed or treated promptly. Any baby with jaundice who develops abnormal muscle tone, high-pitched cry, arching of the back, or who is very difficult to wake for feeds requires immediate emergency assessment.
Key Takeaways
Neonatal jaundice — yellowing of the skin and whites of the eyes in a newborn, caused by elevated bilirubin — is extremely common, occurring in approximately sixty per cent of term newborns and eighty per cent of preterm babies in the first week of life. Most jaundice in healthy term newborns is physiological and resolves without treatment within one to two weeks. A minority of cases require phototherapy (light treatment) to prevent bilirubin rising to levels that could cause brain injury. Jaundice that appears in the first twenty-four hours of life, that is severe, or that persists beyond two weeks (three weeks in breastfed babies) requires prompt medical assessment.
