Cutaneous aging occurs through 2 biologically distinct processes: intrinsic and extrinsic aging. The first is a naturally occurring process that results from slow tissue degeneration. In human dermis, intrinsic aging is characterized by 3 features: atrophy of the dermis due to loss of collagen, degeneration in the elastic fiber network, and loss of hydration. In contrast to intrinsic aging, extrinsic aging is due to environmental factors. Since ultraviolet (UV) exposure is the principal cause of extrinsic aging, it is often referred to as photoaging. At the microscopic level, the distinguishing feature of photoaging is a massive accumulation of elastotic material in the upper and middle dermis, a process termed solar elastosis. Using recombinant DNA technology, it has become possible to demonstrate that UV radiation can activate the human elastin promoter. This provides a mechanism for enhanced elastin biosynthesis, which contributes to the clinical and morphologic changes observed in photoaged skin.