Necrotizing enterocolitis (NEC) is a potentially lethal disease that affects preterm neonates and involves exaggerated intestinal inflammation in response to colonizing bacteria. The incidence of NEC is known to be reduced in infants fed with maternal milk but a new study has now shown that immunoglobulin A (IgA) in maternal milk is a crucial protective factor. By analysing immunoglobulin binding of gut bacteria in faecal samples from preterm infants at the time of NEC diagnosis (n = 30) and age-matched controls (n = 39), a decrease in IgA-bound bacteria was found to be associated with the development of NEC, and maternal milk was found to be the predominant source of IgA in the first month of life. Using a mouse model of NEC, the investigators then confirmed the importance of maternal IgA in preventing the disease by finding that pups reared by IgA-deficient mothers were still susceptible to NEC despite exposure to maternal milk.