Recent information on photoaging mechanisms and the preventive role of topical sunscreen products.

The main environmental element causing photoaging is ultraviolet (UV) light, and this involves an extrinsic mechanism of skin aging superimposed on an intrinsic process. Clinical (evident) characteristics of photoaging include the presence of deep wrinkles, deterioration of skin laxity, and hyperpigmentation. In the UV light spectrum, UVA and UVB radiation cause the most damage in photoaging. UVB light has shorter wavelengths and is mostly absorbed by the stratum corneum, causing erythema and changes in the epidermis, whereas UV rays with longer wavelengths (i.e., UVA) penetrate to the deepest layer of the skin (i.e., the dermis) and interact with DNA. As a result of UV radiation, chemical reactions in the skin produce reactive oxygen species (ROS), which cause protein denaturation, impairment of RNA and DNA synthesis, and damage to the skin structure. Using local sunscreen agents can not only prevent sunburn, but also help prevent photocarcinogenesis and photoaging. Therefore, many epidemiological studies have been conducted with results showing credible and positive evidence for the safety and efficacy of sunscreen to prevent photoaging and photocarcinogenesis.