Jaundice keeps a fair proportion of newborns in hospital an extra day or two and accounts for a lot of readmissions in the first weeks. The yellow is striking and often alarming, but the treatment for it is mature, well-tolerated, and almost always works without complication.
This article covers what phototherapy actually does, when it is used, and the small set of patterns that mean a yellow baby needs urgent attention beyond the standard pathway.
Healthbooq covers newborn health, the routine screens, and the early-weeks decisions families make alongside the medical team.
Why Newborns Get Jaundice
Bilirubin is the pigment left when red blood cells are broken down. Newborns produce a lot of it: high red-cell count, fetal haemoglobin breaking down quickly after birth, and an immature liver enzyme (UGT1A1) that ramps up to full speed only over the first 7–14 days. The mismatch shows in the skin.
Physiological jaundice in term babies appears day 2–3, peaks day 4–5, and clears by day 10–14. In preterm and breastfed babies, it starts a little later and lasts a little longer (up to 21 days is normal in those groups). It moves face-down: face → chest → abdomen → palms and soles. The colour clears from the feet upwards.
Jaundice in the first 24 hours of life is never physiological. The cause is usually red-cell destruction faster than normal — ABO incompatibility, Rhesus disease, G6PD deficiency, hereditary spherocytosis, or congenital infection — and it always needs same-day investigation.
Who Needs Closer Watching
Some babies are more likely to need treatment and tend to be checked more frequently from the start:
- Premature babies (<37 weeks) — immature liver, lower albumin, higher risk
- Babies with significant bruising or a cephalhaematoma at birth — extra red cells to break down
- Mum's blood group O or Rh-negative — ABO/Rhesus risk
- Family history of a sibling who needed phototherapy
- East Asian or Mediterranean heritage — higher physiological jaundice rates and G6PD risk
- Boys — slightly higher rates
- Babies whose feeding hasn't established — under-fed babies clear bilirubin more slowly
- Exclusively breastfed in the first days when supply is still ramping up
Babies in any of these groups have a bilirubin level checked before discharge and a follow-up plan in the first 24–72 hours after going home.
How the Treatment Decision Is Made
The NICE CG98 charts are the answer. Bilirubin is plotted against the baby's age in hours, gestation factored in. The same level — say, 250 µmol/L — means very different things at 24 hours, 48 hours, and 96 hours. The chart, not visual yellowness, decides treatment.
Two ways to get the bilirubin level:
- Transcutaneous bilirubinometer — a small handheld device pressed on the forehead or sternum. Quick, painless, used as a screen.
- Serum bilirubin — heel-prick blood test. The number that decides treatment, especially when the transcutaneous reading is high or the baby is preterm.
Visual assessment of yellowness is unreliable, especially in babies with darker skin tones. Looking yellow is a reason to measure, not a reason to treat or to skip measuring.
What Phototherapy Actually Does
Phototherapy uses light at 460 to 490 nanometres — the blue-green band — to convert unconjugated bilirubin in the skin into water-soluble photoisomers (lumirubin and structural isomers). These can be excreted by the kidneys without needing to be conjugated by the liver. It is mechanism, not magic, and it does not need UV (deliberately so — UV would damage skin).
Two delivery options:
- Overhead LED panel — the most common. Baby in a nappy, eye pads on, lamp 30–50 cm above. The whole skin surface that is uncovered gets exposure.
- Fibreoptic blanket (BiliBlanket) — flexible pad placed under the baby. Delivers slightly less intensive treatment but allows feeding and cuddling on the lamp. Useful for milder cases or as adjunct.
For higher bilirubin levels, double or triple phototherapy uses a panel above plus a blanket below, sometimes plus side panels. More skin exposed, faster clearance.
In practice:
- Baby is undressed to a nappy
- Eye pads on (the bright light is otherwise harmless to skin but can damage retina if eyes uncovered)
- Maximum skin exposure = faster clearance — small nappy, no clothes, no swaddle
- Feeds every 2–3 hours; baby out of the lamp for 15–20 minute feeds, or fibreoptic blanket stays on
- Bilirubin re-checked every 4–6 hours initially
Most babies are off phototherapy in 24 to 48 hours. The bilirubin number drops on a predictable curve, and treatment stops once it is well below the threshold.
Side Effects
Mild and reversible:
- Loose stools — bilirubin leaving the body, as designed. Sometimes greenish.
- Pink rash — light hypersensitivity, fades quickly
- Mild dehydration — if feeds drop off; close attention to feeding mitigates
- Temperature instability — incubator monitoring is standard during phototherapy
- "Bronze baby syndrome" — uncommon, in babies with conjugated jaundice; not actually dangerous, just looks odd. Usually a flag that conjugated bilirubin is high and the underlying picture needs reviewing.
Phototherapy does not cause cancer, fertility problems, eye damage (with eye pads), or any documented long-term harm.
Exchange Transfusion
Reserved for bilirubin that crosses the exchange transfusion threshold despite intensive phototherapy — significantly higher than the phototherapy threshold. The procedure replaces the baby's blood gradually with donor blood through an umbilical or central catheter, halving bilirubin and removing maternal antibodies that may be driving haemolysis.
Exchange transfusion is rare in the UK now — most NICUs do single digits a year. It is essentially always done in the context of significant haemolysis (severe Rhesus or ABO disease, G6PD crisis) where bilirubin is rising too fast for phototherapy alone.
Kernicterus — Why We Bother
The reason for routine screening, the charts, and the lamps is to prevent kernicterus — bilirubin crossing the blood-brain barrier at very high levels and damaging specific brain regions (basal ganglia, hippocampus, brainstem nuclei).
The acute presentation: poor feeding, lethargy, hypotonia or unusual stiffness, arching backwards (opisthotonus), high-pitched cry, in severe cases seizures, coma, death.
The chronic consequences if it happens and the baby survives: athetoid (writhing) cerebral palsy, sensorineural hearing loss, paralysis of upward gaze, dental enamel defects.
Kernicterus is rare in the UK now — single-digit cases per year — almost always in babies discharged early without bilirubin checks, families not given clear follow-up, or jaundice dismissed as "just normal." It is the reason the 14-day jaundice review and the post-discharge bilirubin follow-up exist.
The Other Reason for the 14-Day Check
The other thing the prolonged-jaundice screen catches is conjugated hyperbilirubinaemia. This is a different mechanism: the liver is processing bilirubin into its conjugated form, but it cannot get out into the gut because the bile flow is obstructed.
Causes:
- Biliary atresia — affects about 1 in 15,000–20,000 babies. The bile ducts outside the liver progressively scar shut. The Kasai portoenterostomy operation works far better before 8 weeks of age. Late diagnosis means liver transplant rather than biliary reconstruction.
- Neonatal hepatitis — viral, metabolic, or genetic
- Inherited cholestatic syndromes — Alagille, PFIC
- Metabolic liver disease — galactosaemia, tyrosinaemia, alpha-1 antitrypsin deficiency
- Sepsis affecting the liver
The signs in any jaundiced baby:
- Pale, chalky, putty-coloured stools (the Children's Liver Disease Foundation has a colour chart)
- Dark, tea-coloured urine
Same-day call regardless of how the baby otherwise looks. The baby with biliary atresia often looks completely well in other ways — that is exactly the picture, and exactly why we screen.
A jaundiced baby past 14 days (term) or 21 days (preterm/breastfed) gets a split bilirubin (conjugated and unconjugated fractions). Predominantly unconjugated points to physiological or breast milk jaundice; conjugated points at the list above.
Same-Day Concerns Beyond the Routine Pathway
The list that means don't wait, even if you have a follow-up scheduled:
- Yellow in the first 24 hours
- Yellow on the palms or soles
- Pale stools + dark urine at any age
- Persistent jaundice past 14 days (term) or 21 days (preterm/breastfed)
- A jaundiced baby who is unusually sleepy, refusing feeds, very floppy, arching backwards, or has a high-pitched unusual cry — this is a 999 situation
- A jaundiced baby with fever, mottled skin, or other signs of being unwell
- A breastfed baby with weight loss over 10% who is becoming jaundiced
Key Takeaways
Phototherapy is the standard treatment for jaundice that crosses the NICE CG98 treatment threshold. It uses blue-green light at 460–490 nm — not UV — to convert bilirubin in the skin into water-soluble forms the kidneys can clear without help from the liver. Most babies are off the lamp in 24 to 48 hours. Breastfeeding continues throughout. The treatment threshold depends on the baby's age in hours and gestational age, not on how yellow they look. Pale stools and dark urine in any jaundiced baby are a same-day call regardless of bilirubin level — they suggest conjugated jaundice, with biliary atresia the time-critical diagnosis to rule out.
