Jaundice is a yellowing of a baby’s skin and eyes caused by a buildup of bilirubin, a yellow pigment produced when red blood cells break down. It is the most common condition in newborns, affecting roughly 50% of full-term babies and 80% of preterm babies in the first week of life. In most cases it’s harmless and clears on its own, but high levels of bilirubin can cause serious problems if left untreated.
Why Newborns Are Prone to Jaundice
Before birth, a baby carries extra red blood cells to get oxygen from the placenta. Once the baby starts breathing on their own, those extra cells are no longer needed and begin breaking down rapidly. Each cell releases bilirubin as it’s recycled. In older children and adults, the liver quickly processes bilirubin so it can be excreted in stool. But a newborn’s liver is still maturing. The specific enzymes responsible for processing bilirubin are present at very low levels at birth and take days to ramp up. During that lag, bilirubin accumulates in the blood and stains the skin yellow.
Newborns also reabsorb more bilirubin from their intestines than adults do, a loop that sends bilirubin back into the bloodstream instead of out through stool. This intestinal reabsorption is one reason jaundice can linger, especially in breastfed infants whose stool output is still increasing.
Physiologic vs. Pathologic Jaundice
Most newborn jaundice is physiologic, meaning it’s a normal, expected part of adjusting to life outside the womb. Bilirubin levels typically peak on the third or fourth day of life and then decline over the first week. The yellow tint may be barely noticeable or quite obvious, but it resolves without intervention in most babies.
Jaundice is considered pathologic when it appears within the first 24 hours after birth, when bilirubin levels rise unusually fast, or when levels climb above a certain threshold. Pathologic jaundice signals that something beyond normal newborn physiology is driving the bilirubin up. Possible causes include blood type incompatibility between mother and baby (such as Rh or ABO incompatibility), an inherited enzyme deficiency that makes red blood cells break down faster than usual, infection, or significant bruising from delivery. Babies born before 38 weeks are also at higher risk because their livers are even less mature.
Breastfeeding and Breast Milk Jaundice
There are two distinct types of jaundice linked to breastfeeding, and they have different causes and timelines.
Breastfeeding jaundice shows up in the first week, when milk supply is still being established. If a baby isn’t getting enough milk, fewer stools pass through the intestines, which means less bilirubin leaves the body. The delayed passage of meconium (the dark first stool) makes things worse. The fix is straightforward: more frequent feedings. Breastfeeding should continue, not stop.
Breast milk jaundice is a separate condition that 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. This type is generally mild. If bilirubin levels get high enough to need treatment, phototherapy is the first step. In rare cases, a doctor may suggest temporarily supplementing with formula or expressed breast milk for 12 to 48 hours to confirm the diagnosis and bring levels down.
How to Spot Jaundice at Home
Jaundice follows a head-to-toe pattern. It appears first on the face, especially the forehead, nose, and chin, then spreads downward to the chest, belly, and eventually the arms and legs. One useful technique is the blanching test: gently press a finger against your baby’s skin on the forehead or nose, then release. If the spot looks yellow before the normal color returns, jaundice is present.
In babies with lighter skin, the yellow tint is usually easy to see. In babies with darker skin, check the whites of the eyes (sclera), the gums, the palms of the hands, and the soles of the feet. If yellowing reaches the hands, feet, or whites of the eyes, bilirubin levels may be high enough to need prompt medical evaluation. A baby who is unusually sleepy, feeding poorly, or difficult to wake is also cause for concern regardless of skin color.
How Jaundice Is Diagnosed
Most hospitals screen for jaundice before discharge using a small handheld device pressed against the baby’s skin. This transcutaneous measurement is painless and gives a quick estimate of bilirubin levels. It’s highly sensitive, meaning it’s very good at ruling out dangerous levels. However, if the reading comes back high, a blood draw is needed to confirm the exact number. A blood test (total serum bilirubin) is the definitive measurement used to decide whether treatment is necessary.
Doctors interpret the result based on how many hours old the baby is, not just the raw number. A bilirubin level that’s perfectly normal at 72 hours could be concerning at 24 hours. Risk factors like prematurity, blood type incompatibility, and low albumin (a blood protein that carries bilirubin safely) also lower the threshold for starting treatment.
Phototherapy Treatment
Phototherapy is the standard treatment for jaundice that crosses the threshold for concern. The baby is placed under a special blue-green light, usually wearing only a diaper and protective eye covers. The light penetrates the skin and converts bilirubin into a water-soluble form that the body can excrete through urine and stool without needing the liver to process it first.
For most babies, phototherapy lasts one to two days in the hospital. Bilirubin levels are rechecked periodically during treatment, and the lights stay on until levels drop to a safe range. Feedings continue during phototherapy, and in fact frequent feeding helps because it encourages stool output, which removes bilirubin from the body.
In some cases, babies who have already gone home can receive phototherapy at home using a portable LED device. This option is available for healthy babies born at 38 weeks or later, who are at least 48 hours old, feeding well, have no additional risk factors, and whose bilirubin is only slightly above the treatment threshold. Daily blood draws are still required to track levels.
When Jaundice Becomes Dangerous
Untreated severe jaundice can lead to a condition called bilirubin encephalopathy, where bilirubin crosses from the blood into brain tissue. This is rare but serious. Early warning signs include extreme sleepiness, poor feeding, a weak or absent startle reflex, and low muscle tone. If it progresses, a baby may develop a high-pitched cry, irritability, and a distinctive arched-back posture with the neck extended backward. Late-stage symptoms include seizures, inability to feed, and loss of consciousness.
Permanent brain damage, hearing loss, and death are possible outcomes of untreated bilirubin encephalopathy. This is why newborn jaundice screening exists and why follow-up appointments in the first few days after hospital discharge matter. The vast majority of jaundice cases never come close to these levels, but the consequences of missing severe jaundice are significant enough that every newborn should be monitored.
What Increases a Baby’s Risk
- Prematurity: Babies born before 38 weeks have less mature livers and are more vulnerable to bilirubin’s effects on the brain.
- Blood type incompatibility: When a mother’s blood type differs from her baby’s (Rh or ABO incompatibility), the mother’s antibodies can attack the baby’s red blood cells, causing them to break down faster.
- Enzyme deficiency: G6PD deficiency, an inherited condition more common in males and certain ethnic groups, makes red blood cells fragile and prone to rapid breakdown.
- Significant bruising: A difficult delivery that causes bruising gives the body extra blood to break down, producing more bilirubin.
- A sibling who needed treatment: A family history of significant jaundice increases the chance the next baby will also need monitoring or treatment.
- Exclusive breastfeeding with difficulty establishing feeding: Not because breast milk is harmful, but because low intake in the first days can slow bilirubin clearance.