Why Do Babies Get Jaundice?

What Exactly Is Jaundice in Newborns?

Why do so many newborn babies develop jaundice, and why does their skin take on that distinctive yellow colour in the days after birth? For parents meeting their baby for the first time, it can be worrying to see this change in appearance.

Yet jaundice is one of the most common conditions in the early days of life, affecting more than half of all full-term infants and an even higher percentage of premature babies.

Jaundice occurs when there is a build-up of bilirubin, a yellow pigment formed when red blood cells break down.

In adults and older children, the liver processes bilirubin efficiently, converting it into a form that leaves the body through stools and urine. Newborns, however, face two unique challenges.

First, they are born with a naturally high number of red blood cells, which are replaced more frequently in the first weeks of life. Second, their livers are immature and less efficient at processing bilirubin.

This imbalance between production and elimination leads to higher bilirubin levels in the blood, a condition known as hyperbilirubinaemia.

Although jaundice is often harmless and temporary, it is important to understand why it occurs, how to recognise it, and when it might signal a more serious underlying problem.

Why Does Jaundice Occur in Babies?

The primary reason newborn babies develop jaundice is the immaturity of their liver.

Unlike adults, who have fully developed livers that can handle the constant processing of bilirubin, newborn livers struggle to keep pace in the early days of life.

This is especially true for premature babies, whose liver function is even less developed.

Another contributing factor is the high number of red blood cells present in a newborn. Babies are born with more red blood cells than adults to carry oxygen effectively before birth.

Once the baby is born and begins breathing on their own, many of these excess cells are broken down.

Every time a red blood cell is destroyed, bilirubin is released into the bloodstream. The combination of increased breakdown and slower liver processing creates a build-up.

When bilirubin accumulates, it seeps into tissues, giving the skin and eyes a yellowish appearance. The degree of jaundice depends on how much bilirubin is present and how well the baby’s body can eliminate it.

What Are the Common Causes of Baby Jaundice?

Not all jaundice is the same, and doctors usually classify it into different types depending on the cause.

The most common is physiological jaundice, which is considered a normal part of a newborn’s adjustment. It typically appears between two and four days after birth and clears within two weeks without causing any harm.

Breastfeeding jaundice may occur if a baby is not feeding well in the first few days of life, leading to inadequate fluid intake and fewer bowel movements.

Since bilirubin is excreted through stools, fewer feeds mean it stays longer in the bloodstream.

A separate condition known as breast milk jaundice develops later, often after the first week. It is thought to be linked to substances in breast milk that interfere with the liver’s ability to process bilirubin efficiently.

Although it can last for several weeks, even up to 12 weeks in some babies, it is rarely harmful.

On the other hand, pathological jaundice is caused by underlying medical problems and requires urgent attention. These include:

• Blood group incompatibility, such as Rh or ABO incompatibility, where the mother’s antibodies attack the baby’s red blood cells.
• Infections, including sepsis or urinary tract infections, which disrupt normal liver and blood cell function.
• Thyroid disorders, particularly hypothyroidism, which slows down metabolism and liver activity.
• Inherited enzyme deficiencies, such as glucose-6-phosphate dehydrogenase (G6PD) deficiency or Crigler–Najjar syndrome, which interfere with bilirubin processing.
• Biliary atresia, a rare but serious condition where bile ducts are blocked or absent, preventing bile and bilirubin from leaving the liver.

By distinguishing between these causes, healthcare professionals can determine whether a baby’s jaundice is harmless or a sign of a more serious problem.

When Should Parents Be Concerned About Jaundice?

While many cases of jaundice are mild and resolve naturally, certain warning signs mean medical advice is urgently needed. If jaundice appears within the first 24 hours of life, it is always a red flag and requires immediate investigation.

Parents should also be concerned if the yellowing becomes more intense, spreads quickly across the body, or lasts beyond two weeks in a full-term baby.

Other symptoms that should prompt medical review include extreme sleepiness, difficulty feeding, dark urine, and pale or chalky stools. A high-pitched cry or unusual irritability can also indicate severe jaundice.

These signs matter because untreated jaundice, when bilirubin levels rise too high, can cross into the brain and cause damage. Recognising the signs early helps prevent complications.

How Is Jaundice in Babies Diagnosed?

Diagnosis begins with careful observation. In UK hospitals, babies are checked for jaundice as part of their routine newborn examination within 72 hours. Midwives and doctors look at the baby’s skin, eyes, and gums under good natural light.

Parents are also encouraged to continue checking at home by pressing lightly on the baby’s forehead or nose to see if the skin appears yellow.

When a professional suspects jaundice, further tests confirm bilirubin levels. A bilirubinometer is often the first step, using light reflected from the skin to provide an estimate.

If levels appear high, a small heel-prick blood test is performed to measure the exact amount of bilirubin in the blood serum.

If jaundice persists or is unusually severe, further tests may check for infection, blood group incompatibility, thyroid issues, or inherited conditions. In some cases, imaging or specialist tests are used to rule out bile duct blockages.

How Is Newborn Jaundice Treated?

Most newborns with jaundice require no treatment because bilirubin levels are not high enough to cause harm. For those who do, treatment options are safe and effective.

Phototherapy is the most common approach. The baby is placed under a special type of blue light, which changes the structure of bilirubin in the skin so it can be removed more easily by the liver and kidneys.

During treatment, babies wear protective eye coverings, and feeding breaks are allowed at intervals. In more severe cases, intensified phototherapy using multiple light sources or light blankets may be used.

If bilirubin levels rise dangerously high or do not respond to phototherapy, an exchange transfusion may be required.

This procedure involves gradually replacing the baby’s blood with donor blood, rapidly reducing bilirubin levels. It is performed in neonatal intensive care and is closely monitored.

Feeding support also plays a vital role. Babies with jaundice should feed regularly to help excrete bilirubin. In some cases, extra fluids are given intravenously if dehydration is a concern.

Where jaundice is caused by an underlying problem, such as infection or rhesus disease, additional treatments like antibiotics or intravenous immunoglobulin (IVIG) may be required.

Can Breastfeeding Affect Jaundice in Babies?

Yes, breastfeeding can be linked to jaundice, but it should not discourage parents from continuing. Breastfeeding jaundice usually occurs in the first week when milk supply or feeding technique is still being established.

The solution is to feed more frequently and seek support from health visitors or lactation consultants.

Breast milk jaundice, which can last longer, is thought to be related to natural substances in breast milk that temporarily reduce the liver’s ability to handle bilirubin.

Importantly, this type of jaundice is rarely dangerous and breastfeeding should continue, as its benefits outweigh the risks.

Regular monitoring ensures that more serious causes are not missed.

How Long Does Newborn Jaundice Last?

The duration of jaundice depends on the baby’s circumstances. In full-term infants, it usually clears by two weeks of age. Premature babies often take longer, sometimes up to three weeks, because their livers are less mature.

Breastfed babies can have mild jaundice that persists for several weeks. In rare cases, it may last up to 12 weeks, though this is typically harmless if other conditions have been ruled out.

By this stage, the liver has matured enough to cope with bilirubin production, and the skin gradually returns to a normal tone.

What Are the Risks of Untreated Jaundice?

Although most newborn jaundice is harmless, dangerously high levels of bilirubin can cause a condition called kernicterus, a form of brain damage resulting from bilirubin crossing the blood–brain barrier.

Symptoms of severe jaundice leading to kernicterus include poor feeding, extreme drowsiness, lack of reflexes, high-pitched crying, and seizures.

If untreated, it can cause lifelong complications such as cerebral palsy, hearing loss, vision problems, and learning difficulties.

Fortunately, with regular checks and effective treatments like phototherapy, kernicterus has become extremely rare in developed countries, including the UK.

Table: Typical Bilirubin Levels in Newborns

(Values vary depending on hospital policy; used for general guidance only.)

Conclusion: What Should Parents Do About Jaundice?

Jaundice in newborns is largely the result of the natural transition from life in the womb to life outside it. The combination of many red blood cells breaking down and an immature liver struggling to process bilirubin explains why it is so common.

Most cases are mild, temporary, and harmless, resolving on their own as the baby grows.

However, parents should remain alert to early warning signs, seek advice promptly if jaundice appears within the first day or persists longer than expected, and follow medical guidance for monitoring and treatment.

With modern care, newborn jaundice is a manageable condition that rarely leads to serious complications.

FAQs About Baby Jaundice

Can baby jaundice clear on its own?

Yes, most cases resolve naturally within 10 to 14 days without treatment.

How do doctors measure bilirubin in newborns?

Doctors use a skin bilirubinometer or a heel-prick blood test to check bilirubin levels.

Can sunlight help treat jaundice?

While sunlight can break down bilirubin, it is not a safe or reliable treatment. Phototherapy is much more effective and controlled.

Should breastfeeding be stopped if a baby has jaundice?

No. Breastfeeding should continue, as its benefits outweigh the risks. Extra feeds may be advised.

Why does jaundice last longer in premature babies?

Premature infants have even less mature livers, making bilirubin processing slower.

What are the warning signs of severe jaundice?

Dark urine, pale stools, refusal to feed, worsening yellowing, and unusual lethargy should raise concern.

Can jaundice return after treatment?

It can recur, particularly in breastfed or premature babies, but it is usually mild and temporary.