Effective Skin Hydration Using an Ultra-Micro Liquid Crystal Emulsion Containing Pumpkin Seed Oil and Polysaccharides

Polysaccharides extracted from Japanese pumpkin (Cucurbita maxima Duchesne) possess antioxidant activity and moisturizing effects. To meet the demand for natural skincare, this study aims to develop ultra-micro liquid crystal (ULC) emulsions containing pumpkin seed oil (PO) and Japanese pumpkin polysaccharide (PP). The novelty lies in the synergistic triple-action mechanism of the lipid lamellar structure, emollients and humectants, which together achieve superior moisturization. The formulation is varied by different emulsifiers (Emulgade® PL 68/50 and Olivem® 1000), thickening agents (0.3–0.5% w/w of hydroxyethyl cellulose, xanthan gum, or guar gum), and active concentrations of 2.0–4.0% w/w PO and 0.1% w/w PP. Physicochemical characterization was conducted via polarized light microscopy, particle size analysis, and wide-angle X-ray diffraction (WAXD). Stability was assessed through centrifugation and six heating–cooling cycles, while clinical safety and moisturizing efficacy were evaluated in human volunteers using the Corneometer® and Tewameter®. Polarized light microscopy revealed distinct Maltese cross structures, while WAXD confirmed the presence of α-gel and lamellar (Lα) phases. The ULC emulsion containing PO and PP (F9), comprising 4.5% Emulgade® PL 68/50, 0.3% xanthan gum, 2.0% PO, and 0.1% PP, demonstrated excellent physical stability and a particle size of 4.02 ± 0.02 µm. Clinical results demonstrated that F9 was non-irritating and significantly enhanced skin hydration, while reducing transepidermal water loss compared to the baseline (p < 0.05). Although F9 showed the greatest numerical improvement in barrier function, its efficacy was comparable to placebo cream and ULC emulsion containing PO (F6) (p > 0.05). In conclusion, the successful integration of pumpkin-derived actives into a stable ULC system provides a safe and effective approach for advanced moisturizing skincare applications.