Jaundice is a common condition affecting newborn babies. It’s caused by the overaccumulation of bilirubin, a byproduct created when hemoglobin is broken down by the body. While most cases clear up on their own, jaundice can lead to complications like brain damage if bilirubin levels become too high. Now, a study provides new evidence that certain bacteria transferred to an infant’s gut when breastfeeding could offer protection. Researchers profiled the gut bacteria of over 70 newborn babies at a hospital in China, finding those with very high bilirubin levels hosted lower numbers of 3 breastfeeding-associated bifidobacteria species. The team then explored the effects of these bifidobacteria in rats with elevated bilirubin, finding they have a unique way of working: Instead of fighting jaundice directly, they help shape the composition and function of the entire gut microbe community, encouraging other bacteria to produce beneficial unsaturated fatty acids like arachidonic and docosahexaenoic acid. These fatty acids then inhibit the activity of an enzyme called β-glucuronidase in the intestine, increasing the excretion of bilirubin out of the body by preventing its recirculation back to the liver. These findings provide key new insight into the underlying mechanisms of jaundice in newborns, underscoring the benefits of breastfeeding and paving the way toward new bifidobacteria-based probiotic treatments.