Cesarean Section Versus Vaginal Delivery: Early Microbiome Seeding and Later Hygiene-Related Disease Risk — A Narrative Review

Birth is the first and arguably the most consequential microbial exposure of a human life. During vaginal delivery, the newborn passes through the birth canal and is inoculated with maternal vaginal and perineal microbiota dominated by Lactobacillus, Prevotella, and Bacteroides species; infants born by cesarean section (C-section) bypass this inoculum and are instead colonized mainly by skin and operating-room associated organisms such as Staphylococcus and Corynebacterium. This early divergence, occurring within a narrow developmental window of immune education, has been proposed as one mechanistic bridge linking the modern rise in C-section rates to the parallel rise in allergic, autoimmune, and metabolic conditions predicted by the hygiene hypothesis.