Prior chronic sun exposure decreases the lifespan of human skin fibroblasts in vitro.

The relationship of actinically-induced "premature aging" to chronologic aging was studied in paired fibroblast cultures obtained from the habitually sun-exposed (lateral) and nonexposed (medial) aspects of the arm of eight male donors, aged 41 to 80 years. In each case, the fibroblast strain derived from the medial, nonexposed aspect of the arm underwent more cumulative population doublings than did the paired strain from the lateral sun-exposed aspect, and this discrepancy increased with donor age and severity of clinical aging changes. Hence, chronic sun exposure does accelerate aging in human skin by at least one established in vitro criterion: it decreases the lifespan of cultured fibroblasts. The data underline the difficulty of distinguishing environmental effects from intrinsic aging changes.