Kernicterus can occur when severe jaundice in a newborn baby is not recognised, monitored or treated quickly enough. Although newborn jaundice is common and often clears without causing harm, very high bilirubin levels can become dangerous if doctors, midwives or nurses do not act in time. In rare cases, bilirubin can cross into the brain and cause permanent brain damage.

This can be devastating for families. A baby who develops kernicterus may experience lifelong effects, including cerebral palsy, hearing loss, problems with movement and coordination, and developmental delays. For parents, it can also raise very painful questions about whether earlier checks or treatment could have prevented the harm.

In this guide, we explain when kernicterus usually occurs, how newborn jaundice can become severe, which risk factors should be considered, what treatment should involve, and when medical negligence may have played a role. We also explain how JMW helps families investigate the care their baby received and understand whether they may be able to make a kernicterus claim.

When Does Kernicterus Usually Occur?

Kernicterus usually occurs in the first few days after birth, when newborn jaundice becomes severe and bilirubin levels rise to a dangerous level. In many babies, bilirubin levels are highest between the second and fifth day of life. This means the first week is often the most important period for monitoring, checking and treating jaundice.

In full-term babies, the greatest risk is usually between days two and seven. However, kernicterus can occur later in premature babies, as their bodies may take longer to process bilirubin. Babies who are born early, have feeding difficulties, have bruising from birth, or have a blood group incompatibility may need closer monitoring because their bilirubin levels can rise more quickly.

Kernicterus does not happen simply because a baby has jaundice. Newborn jaundice is very common, and most babies recover without any long-term effects. The concern arises when severe jaundice is missed, when bilirubin levels are not checked, or when treatment is delayed after high bilirubin levels have been identified.

For parents, this timing can be especially distressing to look back on. A baby may have seemed sleepy, difficult to feed or increasingly yellow, only for the seriousness of the situation to become clear later. Where there were signs that a baby’s jaundice was becoming severe, doctors, midwives and nurses should have acted quickly to assess the baby and decide whether treatment was needed.

You can read more about the condition in our guide to kernicterus.

How Newborn Jaundice Can Lead to Kernicterus

Newborn jaundice happens when bilirubin builds up in a baby’s blood. Bilirubin is a yellow pigment that forms when red blood cells break down. This is a normal process, and every baby’s body produces bilirubin. Usually, the liver processes bilirubin so it can leave the body through the baby’s faeces and urine.

In newborn babies, the liver is still developing. This means it may not process bilirubin as quickly as an older child’s or adult’s liver would. This is why many babies develop mild jaundice in the first few days after birth. In most cases, it improves with feeding, monitoring and time.

The risk of kernicterus increases when there is too much bilirubin for the baby’s body to manage. This can happen if the baby’s red blood cells break down more quickly than usual, if the liver cannot process bilirubin effectively, or if poor feeding means the baby is not passing enough bilirubin out of the body.

The most concerning form is unconjugated bilirubin. If levels become very high, this excess bilirubin can cross the blood brain barrier and enter the brain. This can lead to bilirubin encephalopathy, which means bilirubin has started to affect the brain. The earlier stage is known as acute bilirubin encephalopathy. If this is not treated quickly, it can develop into kernicterus, also known as chronic bilirubin encephalopathy.

This is why early checks matter. Doctors, midwives and nurses should take newborn jaundice seriously when it appears early, worsens quickly, spreads across the baby’s body, or appears alongside symptoms such as poor feeding, unusual sleepiness, a high-pitched cry, or floppy or stiff muscles.

The NHS has further information about newborn jaundice, including signs parents should look out for and when to seek medical help.

What Are the Early Signs of Kernicterus?

Kernicterus symptoms may appear within days after birth, often after newborn jaundice has become more noticeable or the baby has become harder to feed or wake. Parents should never be expected to diagnose kernicterus themselves, but doctors, midwives, nurses and health visitors should take these early warning signs seriously.

The early stage of brain involvement is known as acute bilirubin encephalopathy. At this point, urgent treatment may still prevent permanent brain damage. Signs that a baby needs urgent medical assessment can include:

• Extreme sleepiness: the baby may be very difficult to wake or may not respond as expected.
• Poor feeding: the baby may struggle to latch, suck weakly, feed less often or take much smaller amounts than usual.
• Changes in muscle tone: the baby may feel unusually floppy or may become stiff.
• A high-pitched cry: the cry may sound different from the baby’s usual cry and may be difficult to settle.
• Unusual movements or posture: the baby may arch their back or neck, or have unusual eye movements.
• Reduced responsiveness: the baby may seem less alert, less active or less able to interact.

If bilirubin levels remain dangerously high, symptoms can become more serious. A baby may experience seizures, breathing difficulties or a reduced level of consciousness. These signs need emergency medical care.

When acute bilirubin encephalopathy is not treated quickly, it can progress to kernicterus, also known as chronic bilirubin encephalopathy. At this stage, the damage is permanent. Children who have kernicterus may experience cerebral palsy, hearing loss, difficulties with movement and balance, speech and swallowing problems, and developmental delays.

For more detail on what parents may notice, read our guide to the key symptoms of kernicterus every parent should know.

Which Babies Are More at Risk of Kernicterus?

Any newborn baby can develop severe jaundice, but some babies have risk factors that mean their bilirubin levels need closer monitoring. Doctors, midwives and nurses should consider these risk factors when deciding whether a baby needs blood tests, treatment or follow-up after leaving hospital.

Premature birth

Premature babies and preterm infants are more likely to develop jaundice because their livers may not be mature enough to process bilirubin efficiently. They may also be more vulnerable if bilirubin levels rise, because their bodies are still developing.

This means a premature newborn infant may need more regular checks than a baby born at full term. If jaundice appears early or bilirubin levels continue to rise, hospital staff should respond quickly.

Blood group incompatibility

Some babies develop severe jaundice because their blood group is not compatible with their mother’s. This can happen with Rh incompatibility or ABO incompatibility. When this occurs, the baby’s red blood cells can break down more quickly than usual, causing bilirubin levels to rise.

This type of jaundice can develop quickly. Doctors and midwives should consider blood group incompatibility when a baby becomes jaundiced early, appears very yellow, or has blood test results showing high bilirubin levels.

Bruising during birth

Bruising, swelling or birth injuries can increase the amount of bilirubin in a baby’s blood. This is because the body breaks down the baby’s red blood cells in the bruised area, which can create more bilirubin than the baby’s liver can manage.

This may happen after a difficult delivery or an assisted birth involving forceps or ventouse. Where bruising is present, the baby should be closely monitored for developing jaundice.

Feeding difficulties and dehydration

Poor feeding can increase the risk of severe jaundice because bilirubin leaves the body through the baby’s faeces and urine. If a baby is not feeding well, they may not pass bilirubin out of the body as effectively.

Breastfed babies and breastfed newborns may need extra feeding support in the early days if they are struggling to latch or are not taking enough milk. This does not mean breastfeeding itself is unsafe. It means that feeding difficulties should be recognised and managed so jaundice does not worsen.

Genetic and family risk factors

Some babies have genetic or family risk factors that affect how their bodies process bilirubin or red blood cells. These can include G6PD deficiency (a lack of the G6PD enzyme, which protects red blood cells), sickle cell disease and other haemolytic disorders. A family history of severe newborn jaundice may also be relevant.

When these risk factors are known, they should form part of the baby’s care plan. The aim is to identify elevated bilirubin levels early and treat severe jaundice before it can cause bilirubin encephalopathy or brain damage.

You can read more in our guide to the risk factors of kernicterus.

How Should Severe Jaundice Be Monitored and Treated?

Severe jaundice needs prompt monitoring and treatment to reduce bilirubin levels before they become dangerous. Doctors, midwives and nurses should assess the baby’s age, whether they were born prematurely, whether any risk factors are present, and how quickly the jaundice appears to be developing.

Visual checks can help identify neonatal jaundice, but they are not always enough on their own.  A yellow tint indicative of jaundice may be harder to see in some babies, including babies with darker skin tones. This is why healthcare staff may need to check the whites of the baby’s eyes, the gums and the skin under gentle pressure, as well as arranging bilirubin testing where needed.

Checking bilirubin levels

Bilirubin levels can be checked using a small device placed on the baby’s skin. This is known as transcutaneous bilirubinometry. It gives an estimate of how much bilirubin is in the baby’s blood.

In some cases, blood tests are needed. These may measure total serum bilirubin, which shows the overall level of bilirubin in the baby’s blood. Doctors may also look at serum bilirubin in more detail to understand whether the bilirubin is conjugated bilirubin or unconjugated bilirubin.

These results help doctors decide whether the baby needs treatment. There is no single bilirubin concentration that applies safely to every newborn infant. The level must be considered alongside the baby’s age in hours, whether they were born early, and whether there are risk factors such as bruising, poor feeding or blood group incompatibility.

Light therapy

Light therapy, also called phototherapy, is often the first treatment for severe jaundice. The baby is placed under a special blue light that helps break down excess bilirubin in the baby’s skin. This allows the bilirubin to leave the body more easily through the baby’s faeces and urine.

Phototherapy is a common treatment and is usually effective when started quickly. Some babies may need more intensive light therapy if their bilirubin levels are rising quickly or are already high. During treatment, doctors and nurses should continue checking bilirubin levels to make sure they are falling.

Exchange transfusion

If bilirubin levels remain dangerously high, or if there is a serious risk of bilirubin encephalopathy, the baby may need an exchange transfusion. This treatment usually takes place in a neonatal intensive care unit.

During an exchange transfusion, small amounts of the baby’s blood are removed and replaced with donor blood. This helps rapidly reduce bilirubin levels and can also remove antibodies that are causing the baby’s red blood cells to break down too quickly.

An exchange transfusion is only needed in severe cases, but it can be vital where light therapy has not worked quickly enough or the baby is at high risk of brain damage.

Other treatment and support

Some babies need additional treatment depending on the cause of their jaundice. For example, where severe jaundice is linked to blood group incompatibility, doctors may use intravenous immunoglobulin, known as IVIG, to reduce the breakdown of red blood cells.

Feeding support is also important. If a baby is not feeding well, midwives, nurses or feeding specialists should help parents improve feeding and prevent dehydration. In very rare cases where jaundice is linked to serious liver disease, a baby may need more specialist treatment.

Where Does Kernicterus Occur in the Brain?

Kernicterus affects areas of the brain that help control movement, hearing, learning and coordination. This is why the long-term effects can be so wide-ranging.

When excess bilirubin crosses the blood brain barrier, it can damage delicate brain tissue. The areas most often affected include the basal ganglia, which play an important role in movement and posture, and parts of the brainstem, which help control essential functions. Bilirubin can also affect the cranial nerve nuclei, which may contribute to hearing, eye movement and swallowing difficulties.

This type of brain damage is sometimes described as bilirubin induced neurologic dysfunction. Children who live with the effects of kernicterus may experience:

• Cerebral palsy: particularly types that affect muscle tone, involuntary movements, posture and coordination.
• Hearing loss: including auditory neuropathy, where the ear may detect sound but the brain has difficulty processing it.
• Speech and swallowing difficulties: which may mean the child needs support from a speech and language therapist.
• Movement and balance problems: which may affect sitting, standing, walking and day-to-day independence.
• Developmental delays: including difficulties with learning, communication and fine motor skills.

The effects of kernicterus can shape every part of a child’s life. Families may need support from paediatricians, neurologists, audiologists, physiotherapists, occupational therapists, speech and language therapists, teachers and specialist carers.

You can read more about this in our guide to the long-term effects of kernicterus. We have also explained the link between kernicterus and movement conditions in our article on the link between kernicterus and cerebral palsy.

How Long Does It Take for Bilirubin to Cause Brain Damage?

There is no exact timeframe that applies to every baby. Bilirubin levels can rise at different speeds depending on the baby’s age, whether they were born prematurely, whether they are feeding well, and whether they have other risk factors.

Once bilirubin levels become dangerously high, bilirubin toxicity can begin to affect the brain over hours or days. This early stage is acute bilirubin encephalopathy. If the baby receives proper treatment quickly, doctors may still be able to prevent permanent brain damage. If treatment is delayed, acute bilirubin encephalopathy can progress to kernicterus.

This timing is one reason why severe neonatal hyperbilirubinemia should always be taken seriously. Doctors, midwives and nurses should act quickly when a baby has signs of developing jaundice alongside poor feeding, extreme sleepiness, weak sucking, a high-pitched cry, floppy or stiff muscles, or other symptoms of kernicterus.

In a medical negligence claim, JMW investigates whether there were points where bilirubin levels should have been checked sooner, treatment should have started earlier, or a baby should have been referred for urgent hospital care.

When Can Kernicterus Be Linked to Medical Negligence?

Kernicterus is rare, but it is often preventable when severe jaundice is recognised and treated in time. Not every case will involve medical negligence. However, if a child developed kernicterus because doctors, midwives, nurses or health visitors missed clear warning signs or delayed treatment, the family may have grounds to make a medical negligence claim.

Medical negligence may have played a role where there were failures such as:

• Failing to recognise newborn jaundice: for example, not acting when a baby’s skin, eyes or gums appeared yellow.
• Failing to consider risk factors: such as premature birth, bruising, poor feeding, blood group incompatibility, haemolytic disease, sickle cell disease or a family history of severe jaundice.
• Not checking bilirubin levels: including delays in arranging a skin bilirubin check, blood tests or total serum bilirubin measurement.
• Not acting on blood test results: where serum bilirubin levels were high or rising and treatment should have started.
• Delaying light therapy: when phototherapy should have been started sooner to reduce bilirubin levels.
• Delaying an exchange transfusion: where bilirubin levels were dangerously high and urgent treatment in a neonatal intensive care unit was needed.
• Discharging a baby without proper follow-up: especially where jaundice was already visible or risk factors were present.
• Not responding to parental concerns: such as reports of poor feeding, extreme sleepiness, weak sucking, changes in crying or unusual stiffness.
• Poor communication between staff: where important information was not shared between midwives, health visitors, GPs, paediatricians and hospital doctors.

In some cases, the key issue is not one single mistake. It may be a series of missed opportunities. A baby may have had visible neonatal jaundice, known risk factors, rising bilirubin levels and symptoms of kernicterus, but still did not receive treatment quickly enough.

This is why the timing matters. If severe jaundice is treated early, doctors can often reduce bilirubin levels before permanent brain damage occurs. Where there was a delay, a medical negligence investigation looks closely at what should have happened, when it should have happened, and whether earlier action would have changed the outcome.

Clinical negligence claims involving kernicterus often require detailed evidence. This may include maternity records, neonatal records, bilirubin charts, blood test results, discharge paperwork, community midwife notes, health visitor records and evidence from the family about what they noticed at the time.

You can read more about how these cases are investigated in our guide to how to prove medical negligence.