Assumption: All babies have similar microbiota when they are born.
In this study, babies and their mothers were tested for microbes just after birth. The babies who were born vaginally had microbes resembling their mother’s vaginal microbes while those born by cesarean section had microbes resembling their mother’s skin. This could explain why babies born through cesarean section often have immune systems that work differently than those of babies born vaginally.
This was a very small study, but is worth follow-up. There are certainly implications here that could affect babies throughout their lives. For example, most MRSA skin infections on infants occur in babies born via cesarean section. Allergies and asthma are also more likely in children who were cesarean babies. This study begins to answer the question, “Why?”