Abstract
Urban air pollution, characterized by high concentrations of particulate matter (PM2.5 and PM10), heavy metals, and polycyclic aromatic hydrocarbons (PAHs), represents a severe environmental stressor that compromises stratum corneum integrity and destabilizes the cutaneous microbiome. This randomized, double-blind, vehicle-controlled clinical study evaluated the barrier-restorative and microbiome-protective efficacy of a novel topical active combination comprising 3% Lactobacillus ferment lysate (LFL) and 4% niacinamide during acute urban dust exposure. Sixty healthy adult volunteers were subjected to a standardized aerosolized particulate matter challenge on designated volar forearm test sites. Skin barrier recovery was assessed via transepidermal water loss (TEWL) and stratum corneum hydration, while cutaneobiome dynamics were tracked using 16S rRNA gene sequencing. Biomarkers of oxidative stress (malondialdehyde) and inflammation (interleukin-1α and interleukin-8) were quantified from tape-stripped epidermal samples. Results demonstrated that the combination treatment significantly accelerated barrier restoration compared to individual active treatments and the vehicle, reducing post-exposure TEWL elevation by 42.8% within 24 hours (p < 0.001). Microbial profiling revealed that the combined formulation effectively maintained alpha-diversity and suppressed pollution-induced expansions of opportunistic Cutibacterium acnes and Staphylococcus aureus strains, while nurturing commensal Staphylococcus epidermidis populations. Furthermore, inflammatory marker expression was markedly attenuated. These findings demonstrate a clear bi-functional synergy between postbiotic lysates and niacinamide, providing a robust defense strategy for skin health and aesthetic preservation in heavily polluted urban environments.
