Intrinsic aging vs. photoaging: a comparative histopathological, immunohistochemical, and ultrastructural study of skin

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Abstract
Cutaneous aging is a complex biological phenomenon affecting the different constituents of the skin. To compare the effects of intrinsic and extrinsic aging processes, a total of 83 biopsies were collected from sun‐exposed and protected skin of healthy volunteers representing decades from the 1st to the 9th (6–84 years of age). Routine histopathology coupled with computer‐assisted image analysis was used to assess epidermal changes. Immunoperoxidase techniques with antibodies against type I and type III collagens and elastin were used to quantitatively evaluate changes in collagen and elastic fibers and their ultrastructure was examined by transmission electron microscopy. Epidermal thickness was found to be constant in different decades in both sun‐exposed and protected skin; however, it was significantly greater in sun‐exposed skin (P = 0.0001). In protected skin, type I and III collagen staining was altered only after the 8th decade, while in sun‐exposed skin the relative staining intensity significantly decreased from 82.5% and 80.4% in the 1st decade to 53.2% and 44.1% in the 9th decade, respectively (P = 0.0004 and 0.0008). In facial skin the collagen fiber architecture appeared disorganized after the 4th decade. The staining intensity of elastin in protected skin significantly decreased from 49.2% in the 1st decade to 30.4% in the 9th decade (P = 0.05), whereas in sun‐exposed skin the intensity gradually increased from 56.5% in the 1st decade to 75.2% in the 9th decade (P = 0.001). The accumulated elastin in facial skin was morphologically abnormal and appeared to occupy the areas of lost collagen. Collectively, the aging processes, whether intrinsic or extrinsic, have both quantitative and qualitative effects on collagen and elastic fibers in the skin.

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