Multidimensional In Vivo Assessment of Skin Performance Following Repeated Application of a Multi-Step Cosmetic Regimen

Background/Objectives: Topical cosmetic actives are increasingly delivered through multi-step regimens intended to improve skin hydration, barrier function, biomechanical properties, and visible signs of aging. Because the performance of such systems cannot be fully captured by a single endpoint, multidimensional approaches are useful to describe skin responses across complementary instrumental and subjective endpoints. This exploratory study aimed to develop and apply an in vivo assessment framework for evaluating skin changes associated with use of a multi-product topical cosmetic regimen targeting signs of skin aging. Methods: A 30-day exploratory, open-label, uncontrolled study was conducted using a four-step facial routine comprising a serum, an eye contour treatment, a day cream, and a night cream as a model of sequential topical administration. The evaluation integrated instrumental and subjective endpoints, including transepidermal water loss for barrier function, superficial and deep hydration measurements, elastometry for skin elasticity, colorimetric analysis for brightness, Antera® 3D-CS imaging for wrinkles and fine lines, roughness parameters for skin texture, and self-assessment questionnaires for perceived efficacy and cosmetic acceptability. Results: After 30 days of repeated application, statistically significant within-study changes from baseline were observed in transepidermal water loss, superficial hydration, brightness, deep hydration, elasticity, wrinkle length, wrinkle index, fine-line length, fine-line index, and surface roughness. Subject-reported outcomes were consistent with the instrumental results, particularly regarding perceived hydration, smoothness, and overall skin quality. Conclusions: The proposed uncontrolled exploratory multidimensional in vivo framework enabled the descriptive assessment of skin performance changes during repeated use of a multi-step cosmetic regimen. The combined instrumental and self-assessment approach supports a broader characterization of cosmetic-related skin changes in hydration, barrier function, elasticity, texture, and visible signs of aging.