Progress has been made in defining the structural and functional alterations that occur in skin with age. Changes caused solely by longevity have been delineated from changes due to long-term sun exposure. Uneven pigmentation is 1 of the major changes in the gross morphologic characteristics of the aging skin and is much more marked in sun-exposed areas. In the epidermis, melanin pigments are good indicators of photoaging. Ultraviolet radiation plays a major role in the induction of melanocyte aging and may severely damage the melanocyte system of the skin, resulting in both hypermelanotic and hypomelanotic lesions.
Castanet J, Ortonne J. Pigmentary Changes in Aged and Photoaged Skin. Arch Dermatol. 1997;133(10):1296-1299. doi:10.1001/archderm.1997.03890460120015