The Mechanism of Action of Topical Retinoids for the Treatment of Nonmalignant Photodamage, Part 1

Photodamage or photoaging refers to the skin changes that are induced by cumulative exposure to UV radiation and are superimposed on the signs of chronologic aging. Histologically, photoaged skin is characterized by keratinocyte atypia, a loss of polarity (orderly maturation of skin layers), degeneration of collagen, and deposition of abnormal elastotic material. These changes can be attributed to the effects of chronic exposure to UVA, including reduction in the amount of type I collagen in the skin, induction of a low-grade inflammatory response and the enzymes responsible for matrix degradation, and impairment of barrier function.

The 2 main categories of treatment for photodamage include topical agents and resurfacing procedures. The latter includes chemical peels, dermabrasion, and laser resurfacing, all of which can produce rapid results but are also associated with patient downtime, risk for complications, and significant cost. Topical therapies are simple to use but require good adherence to treatment for some months before