It's well-documented that children begin building a microbiome that influences the state of their health from the moment of birth, which is why a choice such as method of delivery (C-section vs. vaginal) and feeding practices (breastfeeding v. formula-feeding) is so important.
The human microbiome is the population of more than 100 trillion microorganisms that live in our gut, mouth, skin and elsewhere in our bodies. These microbial communities have numerous beneficial functions relevant to supporting life. Bacteria in the gut play an important role in health, helping digest food, stimulating the development of the immune system, regulating bowels and protecting against infection. Disruption of the gut microbiota has been linked to a range of diseases, such as inflammatory bowel disease, allergies, asthma, cancer and others.
The microbiome is passed from one generation to the next; the first inoculation received via intra-uterine and vaginal flora, then via breastfeeding and skin-to-skin contact. Researchers found that infants born by cesarean delivery were lacking a specific group of bacteria found in infants delivered vaginally, even if they were breastfed. Infants strictly formula-fed, compared with babies that were exclusively or partially breastfed, also had significant differences in their gut bacteria.