It has been recognized for nearly a century that human beings are inhabited by a remarkably dense and diverse microbial ecosystem, yet we are only just beginning to understand and appreciate the many roles that these microbes play in human health and development. Establishment of the microbiome begins at birth, but many previous studies on infant skin health have focused on Candida species. Little is known on the full microbial composition across different areas and even less is known on how these communities change during disease/inflammatory states. In this clinical study, infants were recruited during periods of diaper dermatitis (DD) and health to characterize the skin microbiome in these two states. Substantial shifts in the skin microbiome were observed across four sites in the diapered area (genitals, intertriginous, buttocks and perianal), as well as during periods of DD. As DD scores increased, there was a shift in relative abundance that demonstrated higher community percentages of faecal coliforms, such as Enterococcus, and lower percentages of Staphylococcus strains. In high‐rash samples, the predominant Staphylococcus species is S aureus, potentially implicating S aureus as a DD aetiological agent. This study provides new information related to the microbiome on infant skin in the diapered area and provides insights into the role of the microbiome in the development of DD.

Dermatitis in the diapered area (DDA) is the most common skin condition in infants and can cause significant pain and discomfort, leading to disturbed sleep, changes in temperament, and heightened concern and anxiety for caregivers. This study investigates the relationship between skin pH, microbiome composition, and DDA severity in 158 infants from China, the US, and Germany, focusing on the buttocks, perianal, and thigh regions. Significant variations in DNA biomass and microbiota profiles were noted. Escherichia coli and Veillonella atypica were linked to higher rash scores and elevated skin pH, while Bifidobacterium longum showed a negative correlation with buttocks pH and rash severity but not with perianal rash. Correlation patterns emerged for other species, like Enterococcus faecalis, between perianal and buttocks rashes. Functional analysis identified key categories, including lipid and fatty acid metabolism, cofactor, amino acid, and carbohydrate metabolism, homeostasis and osmolarity stress, and microbial virulence and oxidative stress response, which are vital for skin health, DDA, and pH regulation in infants. These findings underscore the importance of maintaining a mildly acidic skin pH and minimizing fecal and urine residues for optimal infant skin health, suggesting that microbiota significantly influence DDA development, and provide insights for future preventive strategies and therapeutic interventions.