Red rice extract as a biological UV filter and its photoprotective enhancement effects

This study aimed to comprehensively assess the potential of red rice extract as a biological UV filter and to investigate its ability to enhance SPF performance and partially replace chemical UV filters in sunscreen formulations. Red rice is known for its high levels of bioactive compounds—including phenolic acids (such as ferulic, p-coumaric, and isoferulic acids), flavonoids, anthocyanins, and procyanidins—which possess strong antioxidant and photoprotective properties. However, research on its direct application in UV protection remains limited.

To characterize its photoprotective potential, the UV absorption spectrum of red rice extract was compared with that of three conventional UV filters. The extract exhibited broad-spectrum UV absorption as well as strong photothermal stability, suggesting its suitability as a UV-filtering agent. The total phenolic content was quantified using the Folin–Ciocalteu method, and antioxidant capacity was confirmed via DPPH free radical scavenging analysis, demonstrating robust antioxidative activity that complements UV-filtering effects.

The practical photoprotective performance of red rice extract was further evaluated by incorporating varying concentrations into two sunscreen systems: oil-in-water (O/W) and water-in-oil (W/O). SPF measurements using the UV2000S revealed clear concentration-dependent enhancement. Adding 1% extract increased the SPF value of both formulations by more than 10%, confirming its value as an SPF booster.

Moreover, the study explored the potential of red rice extract as a natural alternative to chemical UV filters. Substitution modeling indicated that 1%, 3%, and 5% red rice extract could replace approximately 12.82%, 19.05%, and 26.09% of conventional UV filters, respectively, while achieving comparable SPF values. This finding underscores its capacity to reduce reliance on chemical filters, which are associated with skin irritation, phototoxicity, and environmental concerns such as coral reef damage.

In summary, this study provides the first comprehensive evaluation of red rice extract’s UV absorption profile, antioxidant activity, and photoprotective performance in real sunscreen formulations. The results highlight its dual function as both a biological UV filter and an effective SPF enhancer. These findings support the use of red rice extract as a safe, natural, and environmentally sustainable ingredient for next-generation sunscreen products.