The ageing dermis: the main cause for the appearance of 'old' skin.

Ageing of the skin is associated with progressive atrophy of the dermis, as well as changes in the architectural organization, leading to folds and wrinkles. As the dermis comprises living tissue, dermal changes are not simply the sum of age-related changes occurring in the mesenchymal cells and the supporting macromolecular structures. Chronological ageing reduces the life of fibroblasts in vitro and, to some extent, in vivo; their potential for division being lower in the elderly. Fibroblasts replicate in vitro but only divide very slowly in vivo. Both endogenous factors, e.g. nutritional and endocrine status, and environmental factors, e.g. UV radiation, toxic compounds or free radicals, affect the functions of fibroblasts and the physical and chemical nature of the supporting macromolecules. Mechanical forces also play an important role in the architectural deterioration of the dermis. In vitro models have been developed using dermal cells and supporting tissue to investigate the factors involved in the ageing process.