From the bottle to the skin: challenges in evaluating antioxidants.

Endogenous production and ultraviolet-generated free radicals in the skin can lead to photoaging and even skin cancer. Topical antioxidants have been found to provide benefits against ultraviolet damage and these ingredients have been incorporated into various cosmetic products and claimed to have substantial effects. Currently, there is a lack in a standardized rating system to measure the concentration and activity levels of antioxidants in these products. As a result, it is difficult for consumers and clinicians to evaluate and select commercial products based on readily accessible evidence. In this review, we will describe four assays which have been used to measure antioxidants in various products, and the strengths and weaknesses of each test will be detailed. We will highlight key considerations for clinicians when interpreting the results of antioxidant tests when evaluating commercial products containing antioxidants.