Probiotic Skin Serum Reshapes Microbiome and Hydration in Dry Skin Trial

Dry skin is a widespread dermatological concern driven by compromised barrier integrity, reduced natural moisturizing factor production, and disrupted skin microbiota—yet few rigorous in vivo studies have examined all three dimensions simultaneously using a validated protocol. This Italian study aimed to fill that gap by evaluating a novel 'Nourish 3-Biotic Rich Serum' containing a combination of prebiotics (alpha-glucan oligosaccharide, fructose, glucose, Polymnia sonchifolia root juice), probiotics (Lactobacillus ferment, Lactobacillus strains), and postbiotics (Sphingomonas ferment extract, fermentation-derived peptides and enzymes) against a matched placebo in women with confirmed facial dryness.

The single-blind, split-face trial enrolled 20 female volunteers aged 28–65. Each participant applied the active serum to one cheek and the placebo to the other twice daily for 30 days, with a mandatory 12-hour washout before each measurement visit. Biophysical assessments at baseline (T0) and day 30 (T30) included stratum corneum water content (Corneometer CM825), transepidermal water loss (TM300W evaporimeter), surface protein content via infrared densitometry tape-stripping (SquameScan), viscoelastic skin properties (DermaLab Combo, parameters R0 for firmness and R2 for elasticity), and 3D topographic roughness (Antera 3D). Skin microbiota was analyzed in 15 of the 20 participants using 16S rRNA metagenomic sequencing (Illumina), following a previously validated tape-stripping collection protocol from the cheeks, with the forehead as a control area. Subgroup analyses were performed by age: younger (<50 years) versus older (>50 years).

On biophysical outcomes, the active serum outperformed placebo across all measured parameters. Stratum corneum hydration increased significantly, TEWL decreased (indicating improved barrier function), and surface protein content fell—a surrogate marker for accelerated cellular turnover and desquamation normalization. Skin firmness (R0) and total elasticity (R2) both improved, and 3D topographic analysis confirmed reduced maximum roughness height. Age-stratified analysis revealed that older volunteers (>50 years) showed more pronounced baseline deficits and correspondingly larger improvements, particularly in elasticity, suggesting the formulation may be especially relevant for age-related skin dryness.

For the microbiome, 16S sequencing revealed that both the active serum and placebo produced some degree of microbiota restoration over 30 days—consistent with the concept that removing barrier-disrupting stressors alone can permit microbial community recovery. However, only the active serum significantly increased the abundance of Cutibacterium acnes, the dominant commensal of sebaceous skin sites that plays a protective role via antimicrobial peptide production and pH maintenance. Equally notable, only the active serum decreased Pseudomonas koreensis, a gram-negative bacterium previously associated with dry and rosacea-type skin conditions, suggesting a targeted rebalancing effect attributable to the prebiotic/probiotic/postbiotic ingredients rather than to carrier excipients.

These findings position 3-biotic cosmetic formulations as promising tools not only for symptomatic moisturization but for actively modulating the skin ecosystem. Caveats include the small sample size, all-female cohort, single-blind rather than double-blind design, and the 30-day observation window, which may be insufficient to capture sustained microbiome shifts. Nonetheless, this study provides a rare combined biophysical-microbiome dataset for dry skin and a validated methodology that future larger trials can build upon.