<![CDATA[Indonesia, as a tropical country, receives high-intensity ultraviolet (UV) radiation, particularly UVB, which can cause erythema, hyperpigmentation, premature skin aging, and skin cancer, while synthetic sunscreens such as oxybenzone and octinoxate may cause irritation, hormonal disruption, and aquatic pollution, creating a need for natural alternatives. Bougainvillea flower (Bougainvillea spectabilis) contains flavonoids, alkaloids, saponins, tannins, and phenolic compounds with potential as antioxidants and UV absorbers. This experimental study aimed to determine the SPF value and physical stability of sunscreen lotion containing bougainvillea flower extract at various concentrations. Flowers were extracted by maceration using 96% ethanol, then formulated into four lotion formulas with concentrations of 0% (F0), 1.5% (F1), 2% (F2), and 2.5% (F3), evaluated through physical quality tests, accelerated stability testing, and in vitro SPF determination using the Mansur spectrophotometric method. All formulas met the quality requirements, with pH 4.70–5.90, spreadability 6.10–6.66 cm, adhesion 5.81–6.59 seconds, viscosity 3,899.0–8,695.3 cPs, an oil-in-water emulsion type, and remained stable over six cycles. The SPF value increased with extract concentration, from 5.83 in F0 to 12.51 in F3, categorized as maximum protection, approaching the positive control SPF of 13.39. These findings indicate bougainvillea flower extract has potential as a natural ingredient for effective sunscreen preparations.]]>
