Breast Milk and Allergic Disease Development: Immunological Factors Associated with Eczema, Food Allergy and Wheezing/Asthma

Purpose of Review Human milk (HM) contains a diverse array of immunological, microbial, and metabolic bioactive factors that may influence early immune maturation and allergic disease susceptibility. This narrative review examines current evidence linking major HM bioactives with eczema, food allergy, and wheezing/asthma, integrating mechanistic findings with human observational and clinical data. Recent Findings Transforming growth factor-β (TGF-β), secretory IgA (sIgA), human milk oligosaccharides (HMOs), cytokines, fatty acids, short-chain fatty acids, the HM microbiome, and extracellular vesicles have all been implicated in pathways relevant to epithelial integrity, microbial colonization, and immune tolerance. However, associations with allergic outcomes are heterogeneous and frequently context dependent. Findings vary according to lactation stage, maternal characteristics, infant susceptibility, microbial exposures, and outcome definition. Mechanistic evidence is often stronger than prospective clinical evidence, and no individual HM component or bioactive profile has yet emerged as a reproducible predictor of allergy protection. Summary Current evidence supports viewing HM as a dynamic maternal–milk–infant biological network rather than as a source of isolated protective factors. Future studies should integrate repeated HM sampling, rigorous allergic phenotyping, and multi-omic approaches to distinguish causal mediators from biomarkers of maternal or infant biology.