Ultraviolet (UV) light represents the major factor in skin photoaging and skin cancerogenesis.1,2 UV exposure causes acute inflammatory changes (such as erythema, edema, and subsequently pigmentation or tanning) and chronic changes (such as immunosupression, photoaging and photocarcinogenesis). Exposure to UV light generates reactive oxygen species (ROS), which are central players in oxidative damage to lipids, proteins and cellular DNA.3,4
The skin possesses a range of enzymatic and non-enzymatic antioxidants charged with protecting the skin against oxidative stress caused by damaging free radicals.5 While these natural antioxidants provide protection of the skin at the intracellular and extracellular level, they are not able to effectively offset excessive production of free radicals induced by UV light and other environmental aggressors.6 Thus, it has been suggested that topical application of antioxidants may be useful in providing protection of the skin against oxidative damage, particularly in the areas where the skin needs additional protection.7
Several in vitro and in vivo studies have clearly demonstrated antiradical potential of different topical antioxidant formulations and their photoprotective efficacy in preventing ROS-induced skin damage.7â€“12
In vitro testing of cosmetic formulations with antioxidants is complex and very often the results achieved in these studies cannot be confirmed in vivo studies. Furthermore, many clinical studies evaluating the efficacy of topical antioxidants are based on the assessment of the prevention of UV-induced erythema and sunburn cell formation.13 However, currently there is no standardized method to evaluate the complex effects of topical formulations combining different antioxidant ingredients.
It has been demonstrated that UV exposure induces the photooxidation of skin surface lipids (SSL) derived from epidermal lipids and from the sebum.14 Thus, evaluation of the major sebum lipid, squalene, may be used for determination of antiradical capacity of topical antioxidants.
The aim of this study was: (1) to assess efficacy of topical antioxidant formulation in prevention of the skin lipid peroxidation in the upper parts of the epidermis of the face and (2) to propose a new in vivo method to determine kinetics of squalene photo-oxidation products (squalene monohydroperoxide, SQmOOH) as a reliable method to evaluate antioxidant capacity of a cosmetic formulation.