[Histomorphometric changes of the skin in rats in relation to age]

Histomorphometric evolution of skin was studied using 74 Wistar rats aged from 2 days to 34 months. Epidermal and dermal thickness, as well as surface density of collagen bundles in the superficial dermis was investigated by image analysis. Average epidermal thickness decreases progressively up to the 4th week, than it remains almost constant. Dermal thickness has a biphasic evolution. It increases rapidly during the first 3 weeks (+166%). This increase is followed by an important decrease (-55%), than dermal thickness increases again and reaches at the age of 1 year 5 times its value at birth. That thickness persists up to the end of life. Surface density of collagen bundles follows the rate of increase of dermal thickness, but variations are less important. Total increase of surface density of dermal collagen bundles between birth and the end of life corresponds to 56% of the initial value.