Skin microbiome and cutaneous aging mechanisms and clinical implications

The skin microbiome is an integral component of the cutaneous ecosystem and contributes to barrier, immune, and metabolic homeostasis. Available evidence is examined across three distinct levels: microbial community structure, functional activity, and host biological response. This ecological-functional distinction is necessary because taxonomic abundance alone does not establish microbial activity, biological effects, or causality. Age-associated microbial variation is considered within the physiological context of cutaneous aging, including reduced sebaceous activity, altered hydration and surface pH, impaired barrier recovery, chronic low-grade inflammation, oxidative stress, and extracellular matrix deterioration. Microbial alterations reported in acne, atopic dermatitis, and rosacea further illustrate how changes in the cutaneous environment can modify host-microbiome interactions and contribute to clinically relevant phenotypes. Translational developments in dermatology and aesthetic medicine include microbiome-compatible skincare, prebiotic and postbiotic formulations, live biotherapeutic approaches, and strategies intended to preserve microbial and barrier recovery after dermatological procedures. Interpretation of the available literature remains limited by low microbial biomass, anatomical and interpersonal heterogeneity, contamination risk, differences in sampling and sequencing methods, and limited functional and longitudinal resolution. Observed microbial remodeling should be interpreted within a bidirectional host-microbiome relationship. Physiological changes that accompany aging can reshape microbial ecology, whereas microbial products may modify barrier and immune responses. Current evidence does not establish whether these microbial alterations are causes, consequences, or correlates of cutaneous aging. Integration of strain-resolved microbiome data with microbial gene expression, metabolite measurements, host molecular responses, and clinical phenotypes will be required to identify biologically relevant microbial functions and determine their value in dermatological practice.