Comparative analysis of human facial skin microbiome between topical sites compared to entire face.

Background: Skin is an essential outer barrier and supports the growth of commensal microorganisms that protects a host from the offense of foreign toxic organisms. With the rapid development of next-generation sequencing (NGS)-based applications, skin microbiome research for facial health care has reached industry growth, such as therapy and cosmetic product development. Despite the acceleration of skin microbiome research, experimental standardization protocol has not yet been established in the facial site and method of sampling.

Objective: Thus, we aimed to investigate the differences in microbial composition at each facial site (cheek, mouth, forehead, and entire face) using comprehensive microbiome analysis.

Methods: Twelve specimens from three men (four specimens per one person) were collected. The hypervariable regions (V3-V4) of the bacterial 16S rRNA gene were targeted for 16S amplicon library construction and classification of bacterial taxonomy. Skin microbial composition for all specimens was investigated, and the differences site-by-site in skin microbial composition were analyzed and evaluated by the various statistical tests.

Results: We were able to validate the independent correlation between the skin microbiome composition and the facial sites. The cheek site showed the highest alpha-diversity in richness and evenness scores compared to the forehead and mouth. The cheek and mouth sites showed a positive correlation (R value > 0.93) with the entire face, while the forehead sites were negatively correlated (R value < 0.2). Given the relative abundance based on statistical correlation analysis, we estimated that the cheek site could be considered an optimal topical site to replace the entire face.

Conclusion: Our study suggests that skin microbiome profiling of four facial sites confirms that the cheek shows the most similar skin flora with the entire face. This study would be informative for preventing bias caused by sampling methods before researching and understanding skin cosmetics development or skin diseases.