Exploration of Changes in the Human Skin Microbiome by Mode of Birth and Following First Bath

BACKGROUND/OBJECTIVES: Microbes colonize the skin soon after birth, and the skin microbiome changes over time. However, the effects of bathing and hygiene products on the infant skin microbiome are not well studied. This randomized, single-center trial analyzed the skin microbiome in neonates born vaginally or via cesarean section (c-section), before and after their first bath with or without a mild baby cleanser. METHODS: One hundred healthy full-term neonates were randomized to baths with water alone or with mild baby cleanser, stratified by delivery mode. Volar forearm swabs of neonates (before and after first bath) and their mothers were analyzed by 16S rRNA metagenomic sequencing. RESULTS: At birth, neonates born vaginally had greater overall richness of the skin microbiome versus those born via c-section. Vaginally delivered neonates had similar species richness as their mothers, while neonates delivered via c-section had much lower species richness. Shannon diversity was similar regardless of birth mode, but community structure varied. Species richness was similar before and after bath in vaginally delivered neonates, but those born via c-section had higher species richness after their first bath and showed larger changes in community structures, compared with the vaginal group. Whether water alone or baby cleanser was used for the first bath did not greatly affect skin microbiome composition. CONCLUSIONS: The mode of birth had the largest effect on the skin microbiome composition, richness, and structure. Neonates born via c-section showed the largest post-bath changes in the skin microbiome, while the use of water or baby cleanser had little effect.