Measurement of biological ageing in human epidermis

Measurements were made of the thickness of the epidermis, the dimensions of keratinocytes and of the surface areas of individual corneocytes in normal human skin from three non‐light exposed sites. The numbers of cells in the epidermis and their height decreased with age, whereas the surface area of individual corneocytes tended to increase with increasing age. The changes demonstrated may be responsible for some of the alterations noted clinically in the skin of elderly individuals. Measurement of tissue ageing is of importance both to the interpretation of the effects of diverse external stimuli and to the study of the effect of dietary and chemical manipulations on the ageing process. Many of the tests devised measure ageing in individual tissues or organ systems and ‘test batteries’ have been employed to obtain an overall assessment of ageing in the organism as a whole (Comfort, 1979). Tests that measure a complex function such as the ‘hand grip strength test’ or determine a biochemical parameter summate the effects of disease, cumulated environmental traumata and true biological ageing and cannot in themselves be used to measure the ageing process. Histometric techniques have the advantage that inspection of the tissue allows identification of the effects of disease and exclusion if the effects of ageing alone are to be considered. They have the disadvantage of any invasive technique and in addition are time consuming. Skin is an ideal organ for the investigation of age dependent changes because of its accessibility. In addition, because of its admixture of tissue types and the different functions that it subserves it is possible to obtain a broad picture of the changes due to ageing. This study attempts to define age related change in overall epidermal dimensions and in parameters of keratinocyte and corneocyte size.