Breastfeeding is the healthiest way to feed newborns and infants. Breast milk is a unique biological fluid, a source of nutrients, immune factors and bacterial flora. Although we know breast milk is one of the factors influencing bacterial flora of the newborn's gastrointestinal tract, the diversity of factors affecting the composition of the microbiota and the biological role of bacteria in human milk is poorly understood. There are several potential factors that influence the composition of the flora of breast milk: immunological disorder of the mother, her diet, antibiotic treatments, birth type, and lactation duration. Currently, there are three known hypothesis about how milk becomes colonized: bacterial transfer from the mother's intestines (endogenous road), colonization after exposure to the bacteria in the birth canal during delivery and the transfer of bacteria from the skin to the breast during breastfeeding. Further research is needed to confirm the validity of the presented hypotheses
