The Bacterial Landscape of Facial Skin: From Homeostasis to Skin Conditions.

The human facial skin microbiome is a complex and dynamic ecosystem that plays a central role in maintaining skin health, immune regulation, and preventing dermatological skin conditions. Cutibacterium acnes (C. acnes) and Staphylococcus epidermidis (S. epidermidis) are the most prominent bacterial species, with shifts in their relative abundance correlating with skin site, age, skin site, and health status. Exploring the facial microbiome offers exciting opportunities, though it requires careful methodological consideration. Sampling techniques vary in invasiveness and depth, which can influence the accuracy and reproducibility of microbiome profiles. While traditional cultivation methods provide valuable insights, they often miss nonculturable microbes, limiting the view of microbial diversity. Molecular approaches such as amplicon sequencing and metagenomics enable a more comprehensive understanding of microbial communities, even though they currently cannot distinguish between viable and nonviable microbes. Addressing these challenges will help unlock the full potential of facial microbiome research. A balanced facial skin microbiome is associated with healthy skin, whereas a dysbiosis of C. acnes and S. epidermidis is commonly observed in acne-prone skin and more pronounced clinically manifest acne. A comprehensive understanding of the diversity and distribution of C. acnes phylotypes, as well as distinct lineages of S. epidermidis associated with skin disorders, is crucial for developing targeted, microbiome-based cosmetic and medical treatments. Emerging strategies aim to restore microbial balance by leveraging the skin's native microbiota, including probiotic approaches. These strategies represent a promising yet still emerging approach, as current clinical evidence remains limited and further well-controlled studies are required, although they may offer benefits by enhancing microbial diversity and supporting skin barrier function.