Photoaging: Update on Pathogenesis, Prevention, and Treatment.

Skin aging is driven by the intrinsic aging process, onto which extrinsic environmental stimuli exert damaging effects. Amongst the external factors, chronic sun exposure contributes the most, and that effect is recognized as photoaging. Clinically, photoaged skin commonly presents with wrinkles and pigmentary changes. Since the first report on the improvement of photoaged skin by topical tretinoin, subsequent investigations have significantly expanded our understanding of this phenomenon. In this narrative review, we adopt a mechanism-driven perspective to discuss the development, manifestations, and treatments for photoaging. We describe the traditional paradigm of ultraviolet radiation-induced extracellular matrix degradation, as well as additional signaling pathways and molecular players that have since been discovered, such as the roles of aryl hydrocarbon receptor, matrix metalloproteinase-2, and nuclear factor erythroid 2-related factor signaling. We describe features of photoaging across skin types, including the increased susceptibility to developing pigmentary alterations in skin of color, along with the role of photoprotection in preventing them. Finally, we review the mechanism and efficacy of common topical, oral, and office-based treatments for photoaging.