<![CDATA[Background: Bougainvillea flowers (Bougainvillea spectabilis Willd.) contain bioactive compounds, including flavonoids, alkaloids, phenolics, saponins, tannins, and terpenoids, which have potential antioxidant properties. Bougainvillea flower extract has been reported to exhibit strong antioxidant activity, with an IC₅₀ value of 82.36 µg/mL. The incorporation of bougainvillea flower extract nanoparticles into peel-off gel masks offers a promising innovation for developing natural antioxidant cosmetic products. Objective: To formulate and evaluate the physical characteristics, stability, preliminary safety, and antioxidant activity of peel-off gel masks containing bougainvillea flower extract nanoparticles. Methods: This experimental study involved extraction by maceration using ethanol, nanoparticle preparation through the chitosan–NaTPP ionic gelation method, and formulation into peel-off gel masks. Evaluations included nanoparticle characterization, physical quality assessment, stability testing, irritation testing, and antioxidant activity determination using the DPPH method. Results: The extraction process yielded 38.13% extract. The nanoparticles exhibited a particle size of 168.54 ± 4.27 nm, a polydispersity index of 0.286 ± 0.019, and a zeta potential of +27.35 ± 1.42 mV. All formulations (F1–F3) demonstrated satisfactory physical characteristics and stability, with no irritation observed under the testing conditions. Formulation F1 exhibited the highest antioxidant activity, with an IC₅₀ value of 16.73 ppm, followed by F2 at 20.93 ppm. All formulations were classified as having very strong antioxidant activity. Conclusion: Bougainvillea flower extract nanoparticles were successfully formulated into peel-off gel masks with satisfactory physical characteristics and very strong antioxidant activity. Formulation F1 demonstrated the highest antioxidant activity and shows potential for development as a natural antioxidant cosmetic product, although further safety and efficacy studies are required.]]>
