Barrier Function and Biophysical Effects of 0.104% and 0.247% Retinol Creams in Mature Facial Skin: A Prospective Study.

Retinol, a bioactive small molecule of the vitamin A family, contributes epidermal and dermal tissue repair through retinoic acid receptor γ (RARγ)/retinoid X receptor (RXR) receptor-mediated transcriptional regulation of keratinocyte differentiation, extracellular matrix (ECM) remodeling, and barrier restoration. However, the relationship between applied concentration, tissue-level regenerative outcomes, and tolerability remains incompletely characterized. This prospective, randomized, single-blind study compared biophysical effects and tolerance of two retinol concentrations in EU-compliant facial creams, high-performance liquid chromatography (HPLC)-verified as 0.104% and 0.247% (w/w). Thirty-eight women aged 40-61 years (Fitzpatrick phototypes II-III) participated across three independent sub-studies: 28 were randomized to either concentration for 12 weeks; 5 underwent split-face ultrasound imaging (0.247% versus retinol-free control) for 8 weeks; and 5 participated in a tape stripping sub-study quantifying stratum corneum interleukin-1 alpha (IL-1α) and interleukin-1 receptor antagonist (IL-1ra) by ELISA before and after 6 weeks of 0.247% retinol treatment. Main cohort assessments included transepidermal water loss (TEWL), hydration, melanin, erythema, pH, sebum, biomechanical parameters, and wrinkle grading. Both concentrations significantly improved barrier parameters-hydration, TEWL, brightness, pH, and sebum-with no inter-group differences. In the ultrasound sub-group, 0.247% retinol increased epidermal thickness (+12.4 μm), epidermal density (+3.84%), and dermal density (+1.81%) versus control, consistent with ECM reorganization and epidermal stratification. Biomechanical parameters showed no significant changes, consistent with retinol's remodeling timeline. Consumer assessment indicated comparable efficacy; 0.247% demonstrated superior smoothing but higher erythema incidence. In the tape stripping sub-study, IL-1α decreased in all participants (median: 25.1 → 13.2 picograms per tape [pg/Tape]; 5/5 concordant), while IL-1ra increased in 4/5 participants (median: 352.8 → 1403.1 picograms per three sequential tapes [pg/3sT]), indicating a directionally consistent shift in the IL-1α/IL-1ra balance; these results are exploratory and require replication in larger cohorts. These findings collectively support clinically meaningful barrier restoration and structural remodeling within current EU safety limits (Commission Regulation EU 2024/996), with 0.104% offering a favorable efficacy-to-tolerability profile for initial therapy.