NONINTRUSIVE TESTING OF SKIN 17 Such a loss of dermatoglyphics may be correlated with a decrease in skin elasticity and an increased tendency to crack and fissure. The underlying events for this change are not completely understood but may be related to atrophic changes in the dermis (4). By changing the nature of the replica material one can obtain information regarding other structural and functional changes in aged skin. For example, the silicone technique as originally devised by Sarkany and Gaylarde (5) and later improved by Harris, Polk and Willis (6) can be used to evaluate sweating. To take an imprint a mixture of silicone base and catalyst (Syringe Elasticon, Kerr) is applied as a thin film immediately after drying the skin surface. Because sweat is immiscible with silicone, each sweat droplet forms a globular hole in the silicone layer. This rubbery sheet can then be peeled off and forms a permanent record for which the density and output of active sweat glands can be estimated. Preliminary results using this procedure suggest that sweating capacity is diminished in older adults (Figure 2). Previous studies by Silver, et al. (7) have indicated that the number of digtal sweat glands visualized by a starch-iodine film technique decreases with advancing age. By using these nonintrusive approaches in conjunction with pharmacological agents known to promote (Pilocarpine) or block (Scopalomine) sweating, additional insight on the nature of the apparent age-related differences in eccrine gland function should be obtained. The skin surface biopsy method of Marks and Dawber (8) results in the removal of a sheet of horny cells from the superficial stratum corneum, usually five to six cell layers. It should be emphasized that this is not a replica technique but actually removes the outermost portion of the horny layer and thus provides biological material which can be subsequently analyzed in a variety of ways. To obtain this sample, one drop of - Figure 2. a) Sweat gland imprint from the volar forearm of the young. Light circles represent perforations in the film of silicone material formed by sweat droplets from functioning sweat glands (x 15). b) Sweat gland imprint from the volar forearm of the old. Note diminished amount of functioning sweat glands (x 15).

18 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 5. Scanning electron micrograph of a skin surface biopsy from the calf of the young. In addition to the easily recognized ridges which constitute the dermatoglyphic pattern, the desquamation of corneocytes in single and small groups can also be resolved (arrows) (x 250). cyanoacrylate adhesive (Aron-alpha, Vigor Co.) is placed on a 3 x ! glass slide which is then pressed against the area to be sampled. After approximately 30 s, the glass slide is removed with its adherent horny layer. This specimen can then be used to study the dermatoglyphic patterns as well as the configuration and patterns of desquamation with the scanning electron microscope (Figure 3). INDIRECT ASSESSMENT OF EPIDERMAL PROLIFERATIVE ACTIVITY Horny cells are continually being lost into the environment due to exfoliation. Normally, the renewal system of the epidermis operates under steady-state kinetics thus for every cell lost, a new cell must be produced in the basal layer. Since all the intervening layers are of a simple transit type, cytokinetic analysis of the stratum corneum provides indirect assessment of epidermal cell proliferation (9,!0). One parameter which can be measured in such a renewal system is transit time, i.e., the time required for a cell to travel through a compartment. Since horny cells are tightly