A Rare Case of Cow’s Milk Protein Allergy in a 12‐Hour Old Neonate With Rectal Bleeding

Hematochezia presenting in the neonatal period requires a thorough exploration of life‐threatening and benign pathologies, including food protein–induced allergic proctocolitis (FPIES). This non‐IgE–mediated food allergy is most commonly associated with cow’s milk protein (CMP). It classically presents in the first weeks to months of life, following the introduction of a cow’s milk–based formula or breast milk where the maternal diet includes cow’s milk. We present a rare case of extremely early onset of CMP‐induced proctocolitis, in a neonate presenting at 12 h of life with hematochezia. How does a food allergy develop at such a young age? We explore the current theories explaining this phenomenon.