Oral N-Acetylneuraminic Acid Promotes Spot Brightening and Enhances Hydration and Elasticity: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Background: N-Acetylneuraminic acid (Neu5Ac), the predominant form of sialic acid, exhibits potent antioxidant, anti-inflammatory, and anti-glycation properties in preclinical studies, suggesting potential dermatological benefits. However, robust clinical evidence supporting the efficacy of oral Neu5Ac supplementation on human skin conditions remains lacking. Methods: A randomized, double-blind, placebo-controlled trial was conducted with 55 Chinese women (40–65 years) who received 120 mg/day Neu5Ac (n = 27) or a matching placebo (n = 28) for 84 days. Skin pigmentation, hydration, biomechanical properties, and dermis echogenicity were evaluated at baseline, D28, D56, and D84 using standardized clinical and instrumental assessments. Results: Both clinical (Pantone color card) and instrumental (photographic) assessments showed that oral Neu5Ac supplementation significantly improved skin lightness on both pigmentary spots and surrounding normal skin compared with placebo at day 84. In addition, stratum corneum hydration and skin biologic extensibility were significantly increased in the Neu5Ac group. Dermal echogenicity showed numerical improvement but did not reach statistical significance. Self-assessment indicated that 100% of the Neu5Ac participants reported improvements in skin whiteness, radiance, elasticity, firmness, and hydration, with mean satisfaction scores of 9.1/10 versus 7.9/10 for placebo. Conclusions: Daily oral supplementation with 120 mg Neu5Ac for 84 days significantly promoted localized spot brightening, enhanced skin hydration, and improved skin elasticity, providing the first clinical evidence supporting Neu5Ac as a safe and effective oral cosmetic ingredient for skin anti-aging.