The most important and well-known theory about skin aging is the free radical theory proposed by Harman.1 Reactive oxygen species such as superoxide radicals and hydrogen peroxide and hydroxyl radicals cause oxidative damage to cellular macromolecules, e.g., proteins, carbohydrates, lipids, etc.2 It has been reported that the appearance of the skin is directly related to its antioxidant concentration—i.e., volunteers with higher concentrations of antioxidants in their skin appeared younger, with regard to furrows and wrinkles.3 Therefore, cosmetic scientists are challenged to develop skin care products that deliver antioxidants into the skin.
Coenzyme Q10 and tocopheryl acetate are well-known antioxidants often used in cosmetic products as anti-aging agents.4, 5 Tocopheryl acetate is an ester that can be converted by enzymes in the skin to α-tocopherol, an active antioxidant.6 Moreover, coenzyme Q10 is reported to protect α-tocopherol from photooxidation via a recycling mechanism.7 Incorporation of these two actives into one product can thus provide synergistic anti-aging activity.8
The objective of the present study was therefore to compare the ability of nanoemulsions and emulsions to deliver coenzyme Q10 and tocopheryl acetate into the skin. Further, since additives such as moisturizers—the mainstay for dry, flaky skin treatments—are necessary in anti-aging products, some test formulations also included rice bran oil, cetyl alcohol, glyceryl stearate and a plant extract blend to provide such a benefit. However, because the plant extract blend was fairly new and composed of several chemicals extracted from Asian plants, its effects on the physicochemical and skin penetration properties of formulations were also evaluated.