BackgroundHuman milk has a high content of the antimicrobial compound hydrogen peroxide (HO). As opposed to healthy full-term infants, preterm neonates are fed previously expressed and stored maternal milk. These practices may favor HO decomposition, thus limiting its potential benefit to preterm infants. The goal of this study was to evaluate the factors responsible for HO generation and degradation in breastmilk.MethodsHuman donors' and rats' milk, along with rat mammary tissue were evaluated. The role of oxytocin and xanthine oxidase on HO generation, its pH-dependent stability, as well as its degradation via lactoperoxidase and catalase was measured in milk.ResultsBreast tissue xanthine oxidase is responsible for the HO generation and its milk content is dependent on oxytocin stimulation. Stability of the human milk HO content is pH-dependent and greatest in the acidic range. Complete HO degradation occurs when human milk is maintained, longer than 10 min, at room temperature and this process is suppressed by lactoperoxidase and catalase inhibition.ConclusionFresh breastmilk HO content is labile and quickly degrades at room temperature. Further investigation on breastmilk handling techniques to preserve its HO content, when gavage-fed to preterm infants is warranted.