Everyone, old and young, is concerned about skin aging, a complex process that can be caused by both intrinsic (chronologic), and extrinsic (environmental) factors. The formation of free radicals is a widely accepted mechanism leading to aging. Free radicals are highly reactive molecules with an odd number of electrons that are generated from oxygen; they cause easy oxidation of other molecules (can extract electrons or hydrogen from, or add oxygen to, another substance). Reactive oxygen species (ROS) initiate signal transduction cascade resulting in up-regulation of AP-1, NF-kB, and down-regulation of transforming growth factor (TGF)-b. Downstream, NF-kb signals increase in interleukin-1 and tumor necrosis factor-alfa levels, and AP-1 activates matrix metalloproteinase (MMP). Decrease in TGF-b expression leads to decrease in collagen synthesis. Cumulatively, these changes lead to increase in collagen breakdown, and increase in elastin production in extracellular matrix, and eventually manifest as the clinical signs of photoaging such as solar elastosis, wrinkles, coarse textures, telangiectasis, and pigmentation.