Collagen loss in photoaged human skin is overestimated by histochemistry

It is well known that photoaged skin is characterized by increases in derma l matrix components that include glycosaminoglycans, proteoglycans and mass es of abnormal elastic fibers accompanied by substantial collagen loss. His tochemical staining of such tissue gives the impression of "massive" loss o f collagen and its replacement by these other matrix components. Early bioc hemical studies have lent support to this notion with a reported decrease i n total collagen of similar to 45% compared to protected skin. More recent studies report considerably less, but varying, amounts of collagen loss, Ra rely have the two approaches, histo-chemistry and biochemical analysis, bee n used in the same study to examine the same tissue. In this study, collage n loss was quantified biochemically in paired biopsies from sun-protected a nd sun-exposed arm skin of moderately photoaged female subjects (age 51-77 years). The values obtained mere compared with histochemical and immunochem ical findings. Quantitatively, collagen loss on a per mg protein basis mas small compared to the histochemical appearance.