Photoaging. Manifestations, prevention, and treatment.

In recent years there has been a growing awareness that many of the so-called attributes of aging skin are, instead, a reflection of environmental assault upon exposed areas of the body. Of special import are the deleterious effects of solar radiation on dermal connective tissue, leading to the visible manifestations of photoaging. Often termed "premature aging," the salient features of the process are distinctly different from those found in normal intrinsic aging. In general, chronically irradiated skin is metabolically hyperactive with epidermal hyperplasia and neoplasia, increased production of elastic fibers, GAGs, accelerated breakdown and synthesis of collagen, and enhanced inflammatory processes. In contrast, protected aged skin is usually characterized by a slow decline in many of these components. Experimental studies with animal models have confirmed the notion that the shorter, more energetic portion of the ultraviolet spectrum (UVB) is responsible for the dermal connective tissue destruction observed in photoaged skin. More recently, it has been shown that UVA and infrared radiation contribute significantly to photoaging, producing, among other changes, severe elastosis. Because the three broad wavebands are inseparably linked in terrestrial sunlight, all are of concern in the photoaging of human skin. Photoaged skin has been thought to be irreversibly damaged. However, our findings indicate that destruction and repair go on simultaneously under continued assault by actinic radiation. The balance is shifted toward repair when the radiation stress is relieved. Both epidermis and dermis are capable of moderate self-restoration when exogenous injury ceases, either by avoidance of sunlight or by the use of broad-spectrum, high-SPF sunscreens. Repair of the dermis, characterized by broad regions of new collagen deposited subepidermally, can be pharmacologically enhanced by topical application of retinoic acid. Although early protection from sunlight, before severe photodamage occurs, is most desirable, it is deemed advisable to counsel even older persons with photoaged skin to adopt protective measures, thereby allowing repair processes to occur.