Elastic fibers in normal human skin. Variations with age: a morphometric analysis

A quantitative study of dermal elastic fibers was carried out by computerized digital image analysis. Sections of skin biopsies taken from the upper inner arm of 33 healthy women and 38 healthy men were stained by a selective procedure for elastic fibers. The Leitz texture analysis system (Leitz-Tas) and mathematical morphology were used for the evaluation of the data. Distinct programs were used for the vertical superficial elastic fibers and for the mature elastic fibers of the reticular dermis. For elastic fibers of the superficial dermis there was no significant variation with age or sex for total area occupied by the fibers or for the total number of fibers per unit skin area or total fiber length. The distribution of the relative fiber number as a function of their length showed that about 80% of the fibers had a length of 0-20 microm, with no detectable age- or sex-dependent variation. The distribution of fiber number frequency as a function of fiber diameter did not show any significant variation with sex or age, either. The relative area of mature elastic fibers increased significantly with age after the sixth decade of life. The total number (Nt) of these fibers did not show however any significant variation with age or sex: Nt per mm(2) of skin surface was 3220+/-660 (S.D.). We found for all age groups a significant increase of total fiber length by comparing persons between 20 and 30 years with those above 60 years. There was, however, no significant variations according to age or sex for the frequency distribution of mature elastic fiber length and diameter. As a significant decrease with age of the dermal thickness was also found in males and females, the loss of elastic fibers with age is mainly due to a loss of skin thickness (skin volume) with age. This loss is about 30% at 50 years and nearly 50% at 80 years. Loss of skin elasticity with age can be due to loss of cells (fibroblasts), to a decrease of their biosynthetic activity and to qualitative modifications of extracellular matrix macromolecules.