Comparative Study to Evaluate the Efficacy and Tolerance of a New Retinoid Combination with the Equivalent Retinol Concentration in the Treatment of Skin Aging

(1) Background: Retinol has consistently demonstrated efficacy in improving signs of skin aging. However, recent European Union regulations have limited its cosmetic concentration to 0.3%, creating the need for new formulations to be capable of maintaining high efficacy, safety, and tolerance. (2) Material and Methods: This clinical study aimed to evaluate and compare the rejuvenating effects and tolerance of a 0.5% retinol serum with a new equivalent technology, Retinduo®, which previously showed promising preclinical results. A single-center, prospective, randomized, controlled, double-blind, two-arm parallel study was conducted in 40 Caucasian women aged 38–60 years with moderate photoaging (Glogau II). 20 participants applied Retinduo® serum and 20 applied retinol 0.5%, following a progressive ap-plication protocol. Clinical and instrumental assessments measured hydration, firmness, elasticity, tone homogeneity, melanin levels, skin roughness, wrinkle parameters, and stratum corneum thickness. (3) Results: Both formulations signifi-cantly improved hydration, firmness, and elasticity from day 28 onward. Retinduo® showed a significant increase in viscoelasticity (R8) from day 56, while retinol 0.5% did not demonstrate significant changes in this parameter. Melanin reduction was observed with Retinduo® at days 28 and 56 and with retinol 0.5% just at day 28. Although a reduction in melanin was observed with both ingredients, the reduction was more significant with Retinduo® at 56 days. Both treatments reduced the thickness of the stratum corneum; however, with Retinduo®, a significant and more pronounced reduction was achieved after 3 months of treatment (30% (p=0.0001) vs. 12% (p=0.033). Retinduo® demonstrated significant wrinkle depth reduction at day 28 and in wrinkle amplitude (width and length of wrinkles) at the end of treatment, while 0.5% retinol showed a positive trend in this parameter. Both products exhibited excellent tolerance. (4) Conclusions: Overall, Retinduo® achieved comparable or slightly superior anti-aging effects while aligning with current European regulatory limits.