Formulation Stability of Sunscreens with Passion Fruit Seed and Paracress Extracts

Growing consumer demand for sustainable cosmetics has stimulated the integration of plant‑derived multifunctional actives into sunscreens. Piceatannol, a stilbene with potent antioxidant, anti‑inflammatory, and photoprotective activities, can potentially enhance UV protection, limiting the concentration of conventional filters. This work assesses the physicochemical compatibility of piceatannol-rich extract in oil-in-water emulsions combined with organic or inorganic UV filters, along with a spilanthol-rich extract incorporated as a putative penetration enhancer. Formulations were characterized by analytical centrifugation, UV-Vis spectroscopy, differential scanning calorimetry, thermogravimetric analysis and accelerated freeze-thaw cycling. Emulsions containing only organic filters remained physically stable, though the filters lowered the volatilization onset by ca. 10 °C. In contrast, inorganic filters provoked immediate darkening, phase instability, and rapid degradation of the bioactives: piceatannol and spilanthol contents fell drastically upon preparation. After 12 days of thermal cycling, piceatannol retention was 40% in the placebo base but became undetectable in all UV‑filter formulations, while spilanthol persisted at only 34% in mineral‑filter systems. These findings demonstrate a pronounced incompatibility between piceatannol/spilanthol extracts and inorganic sunscreens, underscoring the need for alternative delivery strategies, such as encapsulation, surface‑modified minerals or alternative formulations design, to preserve natural actives and achieve truly multifunctional, eco‑conscious sun care.