Aging of the skin connective tissue: how to measure the biochemical and mechanical properties of aging dermis.

The connective tissue of the skin is composed mostly of collagen and elastin. Collagen makes up 70-80% of the dry weight of the skin and gives the dermis its mechanical and structural integrity. Elastin is a minor component of the dermis, but it has an important function in providing the elasticity of the skin. During aging, the synthesis of collagen gradually declines, and the skin thus becomes thinner in protected skin, especially after the seventh decade. Several factors contribute to the aging of the skin. In several hereditary disorders collagen or elastin are deficient, leading to accelerated aging. In cutis laxa, for example, elastin fibers are deficient or completely lacking, leading to sagging of the skin. Solar irradiation causes skin to look prematurely aged. Especially ultraviolet radiation induces an accumulation of abnormal elastotic material. These changes are usually observed after 60 years of age, but excessive exposure to the sun may cause severe photoaging as early as the second decade of life. The different biochemical and mechanical parameters of the dermis can be studied by modern techniques. The applications of these techniques to study the aging of dermal connective tissue are described in detail.