Jaundice, the yellowing of the skin and eyes, is a common occurrence in newborns, affecting a majority of full-term infants in the first week of life. This discoloration happens because of an excess of bilirubin, a yellow pigment created during the normal breakdown of red blood cells. The newborn’s immature liver often struggles to process this pigment quickly, leading to a temporary buildup in the blood. Breast milk jaundice (BMJ) is a specific, generally harmless variation of this common newborn condition, characterized by its later onset and prolonged duration in healthy, breastfed babies.
Defining Breast Milk Jaundice
Breast milk jaundice is characterized by its timing, typically appearing after the initial surge of bilirubin subsides, usually developing four to seven days after birth. This timing separates it from physiological jaundice, which peaks around days three to five, and breastfeeding jaundice, which is an early-onset issue related to insufficient milk intake. Infants with true breast milk jaundice are generally healthy, thrive, and show appropriate weight gain, with normal urine and stool output. The condition is a diagnosis of exclusion, confirmed only after ruling out more concerning causes of prolonged hyperbilirubinemia. It affects 2% to 4% of breastfed infants who have elevated bilirubin levels at three weeks of age.
The Biological Mechanism
Bilirubin elimination involves the liver linking the fat-soluble pigment to a sugar molecule—a process called conjugation—to make it water-soluble for excretion in the stool. Breast milk jaundice interferes with this pathway by promoting the re-absorption of bilirubin from the gut back into the bloodstream, known as enterohepatic circulation.
A frequently cited factor is the presence of the enzyme beta-glucuronidase in some mothers’ milk, which is also naturally present in the infant’s intestines. This enzyme “un-links” the conjugated bilirubin, converting the pigment back into its fat-soluble, unconjugated form. Since unconjugated bilirubin cannot be excreted, it is reabsorbed through the intestinal wall, returning to the blood and contributing to the prolonged discoloration. Other factors, such as higher levels of certain growth factors or nonesterified fatty acids in breast milk, may also inhibit the liver’s ability to conjugate bilirubin.
Diagnosis and Monitoring
Diagnosis begins by measuring the infant’s bilirubin level, typically using a non-invasive transcutaneous bilirubin (TcB) meter on the skin. If the TcB reading is high, a total serum bilirubin (TSB) level is measured via a blood test for definitive assessment. The TSB test differentiates between unconjugated hyperbilirubinemia, characteristic of breast milk jaundice, and conjugated hyperbilirubinemia, which suggests more serious liver disorders. For infants jaundiced at three to four weeks, measuring total and fractionated bilirubin is recommended to rule out cholestasis.
Monitoring focuses on the infant’s overall condition, particularly feeding, hydration status, and weight gain to ensure adequate intake. The primary clinical management is to encourage more frequent breastfeeding, which increases calorie and fluid intake and promotes bowel movements to excrete bilirubin. If bilirubin levels exceed age-appropriate thresholds set by pediatric guidelines, phototherapy is the standard treatment. Phototherapy uses special light to change the bilirubin molecule into a water-soluble form that the body can excrete without liver processing.
In rare cases where bilirubin levels are nearing very high, dangerous levels, a temporary 12- to 48-hour interruption of breastfeeding may be recommended as a diagnostic trial. If the bilirubin level drops significantly—a reduction of at least 2 to 3 mg/dL—it supports the diagnosis of breast milk jaundice, and breastfeeding is quickly resumed. However, interrupting breastfeeding is usually avoided due to its potential negative impact on the breastfeeding relationship.
Duration and Long-Term Outlook
The prognosis for infants with breast milk jaundice is excellent, as it is a self-limiting condition that resolves spontaneously without lasting complications. While physiological jaundice resolves within the first two weeks, breast milk jaundice persists longer, often lasting for 3 to 12 weeks. In some cases, infants may show signs of jaundice for up to four months.
When monitored and managed appropriately, breast milk jaundice does not lead to kernicterus, the permanent brain damage caused by extremely high, untreated bilirubin levels. Continued breastfeeding is strongly recommended throughout the condition, as the benefits of breast milk far outweigh the temporary nature of the jaundice. Healthcare providers reassure parents that the baby is healthy and the discoloration will fade as the infant’s liver matures.