NONINTRUSIVE TESTING OF SKIN 23 Figure 6. a) Sticky slide from shin area of young. b) Sticky slide from shin area of older subject with a dry skin problem. the corneocytes with the light microscope. The appearance of corneocytes from a healthy young subject is shown in Figure 7. Note that these cells lack nuclei, one of the results of the terminal differentiation of epidermal cells (20). These cells also tend to be polygonal in shape with relatively smooth borders. They show lines at the periphery corresponding to regions of overlap with adjacent cells indicating a highly structured epidermis. With advancing age, increased frequency of atypical cells (Figure 8) which lack these general features can be observed. Although clinical significance of these unusual cell types is still uncertain, there can be no doubt that these cytomorphological alterations have diagnostic importance. Indeed, these specimens are akin to those used for Pap Smear cytodiagnosis and exfoliative examination of the skin should be equally as rewarding. Our studies also indicate that changes in corneocyte size may permit a sensitive evaluation of altered skin physiology, especially epidermopoiesis. By using the projected area feature of the Vickers M-85 microcpectrophotometer, changes in corneocyte size can be rapidly and precisely measured (21). Table III gives the results obtained for the volar forearm and upper inner arm sites. Note that for both age cohorts, the volar forearm cells tend to be smaller than those of the upper inner arm. In fact, a size gradient of increasing cell size exists as one goes from the wrist to the axilla. Thus, extreme caution should be exercised to sample specific sites if corneocyte size is to be a meaningful measurement. In this manner an age-related increase in cell size at these two sites has been demonstrated (15). Previous studies by Piewig, et al. (22) have also shown similar age-associated changes in corneocyte size however, we have been unable to confirm any sex differences in this parameter.

24 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 7. Light micrograph showing the morphology of a normal exfoliated corneocyte. It should be noted that with advancing age, there is an increased variance of cell size measurements among the subjects. Figure 9 shows projected area measurements of volar forearm cells from another panel of subjects of various ages. Note that the values are fairly tightly clustered in the early years and exhibit a much wider range later. What Figure 8. Light micrograph showing the morphology of some atypical exfoliated corneocytes.