Jaundice in newborns is a yellow discoloration of the skin and eyes caused by a buildup of bilirubin, a pigment the body produces when it breaks down old red blood cells. It’s extremely common, appearing in roughly 60% of full-term babies during their first week of life. In most cases it resolves on its own, but high bilirubin levels can be dangerous, so knowing what to watch for matters.
Why Newborns Get Jaundice
Bilirubin is the end product of a normal recycling process: when red blood cells reach the end of their lifespan, the body breaks them down and salvages the iron. The leftover waste becomes bilirubin, which the liver converts into a water-soluble form so it can be excreted through stool and urine.
Newborns are uniquely prone to bilirubin buildup for several reasons. They’re born with a high concentration of red blood cells, and those cells have a shorter lifespan than adult red blood cells, so they produce more bilirubin per pound of body weight. At the same time, a newborn’s liver is immature. The enzyme responsible for converting bilirubin into its excretable form is underdeveloped in the first days of life, meaning bilirubin accumulates faster than the liver can process it. This combination creates a temporary bottleneck that resolves as the liver matures over the first one to two weeks.
How to Spot It
Jaundice follows a predictable pattern on the body. It appears first on the face and neck, then spreads downward to the chest, lower abdomen and thighs, then the arms and lower legs, and finally the palms and soles. The further down the body the yellow color extends, the higher the bilirubin level. If you only see yellowing on your baby’s face, levels are likely mild. Yellow skin reaching the hands and feet suggests levels are significantly elevated.
You can check by gently pressing on your baby’s forehead or nose with a fingertip. When you release, the skin briefly appears lighter before color returns. If the underlying skin looks yellow rather than its normal tone, that’s jaundice. In babies with darker skin, the yellowing is often easiest to see in the whites of the eyes, the gums, or the palms and soles.
Most newborn jaundice appears between days two and four of life, peaks around days three to five, and fades within one to two weeks.
Breastfeeding and Jaundice
Two distinct types of jaundice are related to breastfeeding, and they have different causes and timelines.
Breastfeeding jaundice (sometimes called suboptimal intake jaundice) shows up in the first week, when milk supply is still being established. If a newborn isn’t getting enough milk, stool output drops. Since bilirubin leaves the body through stool, less feeding means bilirubin gets reabsorbed from the intestines back into the bloodstream. It also delays the passage of meconium, the dark first stool that’s packed with bilirubin. The fix is more frequent feeding, not less. In most cases, breastfeeding should continue, with eight to twelve feedings per day to keep things moving.
Breast milk jaundice is a separate condition that typically appears in the second week or later and can persist for several weeks. The exact cause isn’t fully understood, but substances in breast milk may slow the liver’s ability to process bilirubin. It’s generally harmless and resolves on its own, though phototherapy or temporary supplementation with expressed breast milk, donor milk, or formula is occasionally used if levels climb too high.
Risk Factors for Severe Jaundice
While mild jaundice is normal, certain factors raise the odds that bilirubin will reach levels needing treatment:
- Blood type incompatibility: When a mother’s blood type differs from her baby’s (particularly Rh or ABO incompatibility), the mother’s antibodies can cross the placenta and accelerate the destruction of the baby’s red blood cells, flooding the system with bilirubin.
- Prematurity: Babies born before 38 weeks have even less mature livers, making them slower to clear bilirubin. The 2022 American Academy of Pediatrics guidelines use gestational age as a key factor in determining treatment thresholds.
- Significant bruising from birth: Bruises contain pooled blood that the body must break down, adding to the bilirubin load.
- A sibling who needed jaundice treatment: Genetic variations in bilirubin-processing enzymes run in families.
- East Asian or Mediterranean descent: Certain ethnic backgrounds carry higher rates of enzyme variants that slow bilirubin metabolism.
How Doctors Measure Bilirubin
Hospitals routinely screen newborns for jaundice before discharge, typically using one of two methods. A transcutaneous bilirubinometer is a handheld device pressed against the baby’s skin that estimates bilirubin levels using light. It’s painless and gives results instantly, and research shows its sensitivity for detecting significant jaundice ranges from 74% to 100%, making it a reliable screening tool. However, a high reading on this device needs to be confirmed with a blood test.
The blood test, called a total serum bilirubin (TSB), is the gold standard. Normal bilirubin in an adult is 0.1 to 1.2 mg/dL. Visible jaundice in a newborn appears around 2.0 mg/dL. Doctors plot the result against the baby’s age in hours on a standardized chart to determine whether the level is in a low-risk, intermediate, or high-risk zone. That placement, combined with gestational age and any risk factors, determines whether treatment is needed.
How Phototherapy Works
Phototherapy is the primary treatment for newborn jaundice. Your baby lies under blue-spectrum lights (or on a fiber-optic blanket) wearing only a diaper and protective eye shields. The light penetrates the skin and triggers two chemical reactions in the bilirubin molecules sitting in the tissue. The most important one, photoisomerization, rearranges the shape of the bilirubin molecule so it becomes water-soluble. In this new form, bilirubin can be excreted through bile and urine without needing the liver enzyme that’s underdeveloped in newborns. It essentially bypasses the exact bottleneck causing the problem.
Phototherapy sessions typically run continuously, with breaks for feeding. Most babies need one to two days of treatment, though some require longer. Bilirubin levels are rechecked every few hours to track progress. Side effects are minimal: loose greenish stools (the bilirubin leaving the body), mild dehydration from increased water loss through the skin, and occasionally a harmless temporary rash.
In rare cases where bilirubin levels are extremely high or rising too fast for phototherapy to keep up, a blood exchange transfusion may be needed. This involves gradually replacing the baby’s blood with donor blood to rapidly lower bilirubin concentrations.
When Jaundice Becomes Dangerous
At very high levels (typically 25 mg/dL or above), bilirubin can cross into the brain and cause a condition called kernicterus, a form of permanent brain damage. Before reaching that point, a baby may show signs of acute bilirubin encephalopathy, the reversible early stage of brain injury. Warning signs include:
- Extreme sleepiness or difficulty waking the baby
- High-pitched, inconsolable crying
- Poor sucking or refusal to feed
- Backward arching of the neck and body
- Fever
These symptoms require immediate medical attention. Kernicterus is preventable with timely treatment, which is why universal screening and close follow-up in the first week of life exist. If your baby’s skin is becoming more yellow, especially on the belly, arms, or legs, if the whites of the eyes look yellow, or if your baby seems unusually hard to rouse or is feeding poorly, contact your pediatrician right away. Jaundice that appears within the first 24 hours of life is never considered normal and always warrants urgent evaluation.