A hypothetical explanation for the aging of skin. Chronologic alteration of the three-dimensional arrangement of collagen and elastic fibers in connective tissue.

To provide a morphologic basis for a better understanding of the "aging" of human skin, the authors studied the three-dimensional arrangement and chronological alterations of the fibrous components of the connective tissue using rats aged 2 weeks to 24 months with a new technique for scanning electron microscopy. These studies showed that with postnatal growth there was a dynamic rearrangement of the collagen and elastic fibers: an ordered arrangement of mature collagen bundles was attained by producing a distortion of the elastic fiber meshwork of relatively straight fibers. During adulthood, there was a subsequent tortuosity of the distorted elastic fibers coupled with an incomplete rebuilding of the elastic fiber network, laid down in a form to interlock with the collagen bundles. These changes provide a model for explaining manifestations of aged skin, such as laxity, sagging, and wrinkling. The tortuously fixed elastic fibers imply that they have been stretched and have lost their original elasticity and ability to restitute short and straight. Interlocking of both collagen and elastic fibers should disturb the two independent fibrous systems, as would normally be the case, and thus decrease tissue compliance.