Development, Stability, and Clinical Efficacy of an Oil-in-Serum Formulation with Olive Extract Standardized in Hydroxytyrosol for Post-Inflammatory Hyperpigmentation Treatment.

Post-inflammatory hyperpigmentation (PIH) is a prevalent dermatological condition arising from inflammatory processes that significantly impacts quality of life. Natural alternatives to conventional treatments are increasingly sought to minimize adverse effects while maintaining efficacy. This study aimed to develop and evaluate an innovative oil-in-serum formulation containing olive extract standardized in hydroxytyrosol (HT) for PIH treatment, assessing its stability, sensory properties, and clinical efficacy. Two complementary formulations were developed: a hydroxyethylcellulose-based gel (with/without 0.1% olive extract containing 20% HT) and an olive oil-based formulation. Stability tests, texture analysis, sensory evaluation and clinical efficacy analysis in participants with PIH were conducted. Overall, the formulations were stable and showed favorable sensory properties. The oil-in-serum system exhibited enhanced spreadability, hydration perception, and reduced stickiness compared to individual components. After 45 days of application, the formulation with HT increased stratum corneum water content and reduced transepidermal water loss (TEWL), indicating improved skin barrier function. A significant reduction in color difference between lesional and perilesional areas was observed in high-resolution imaging analysis, showing a reduction in the PIH. Participants reported enhanced skin hydration and reduced dark spots, which corroborate the instrumental measurements results. Finally, the oil-in-serum formulation with olive extract standardized in HT proved effective for PIH treatment, combining excellent sensory properties with clinical efficacy in improving skin hydration, barrier function, and hyperpigmentation control.