The Effect of Surfactant Combination on the Characteristics, Stability, Irritability, and Effectivity of Astaxanthin Nanoemulsion as Anti-Ageing Cosmetics

Astaxanthin is a xanthophyll carotenoid with antioxidant activity. The topical application of astaxanthin can enhance collagen density. However, its penetration into the skin is limited. Therefore, a delivery system, such as nanoemulsion, is needed. One factor influencing nanoemulsion formation is the selection of the type and concentration of surfactant. This study aims to determine the influence of surfactant combinations: Tween 80-Span 20 (F1), Tween 80-Span 60 (F2), and Tween 80-Span 80 (F3) in HLB system 14 on the characteristics, stability, irritability, and effectivity of astaxanthin nanoemulsion as an anti-ageing cosmetic. The nanoemulsion was prepared using the phase inversion composition (PIC) method. The pH values for all three formulas were within the range of normal skin pH (4-6), viscosity followed the order F1<F3<F2, droplet size F1<F3<F2, PDI for all three formulas was below 0.2, turbidity F3<F2<F1, %transmittance F3>F2>F1, interfacial tension F1<F3<F2, and zeta potential for all three formulas fell within the range of ±30 mV. Real-time tests showed that F3 was the most stable formula. All three formulas remained stable after centrifugation, did not cause irritation, and were able to enhance collagen density and skin elasticity in the order of F3>F1>F2. The characteristics of all three formulas meet the criteria for nanoemulsions with droplet sizes below 50 nm and polydispersity index (PDI) below 0.2 and without skin irritation. The Astaxanthin nanoemulsion with Tween 80-Span 80 (F3) surfactant combination was the most stable with better effects. Therefore, it has the potential for further formulation into anti-ageing cosmetic preparations.