NONINTRUSIVE TESTING- OF SKIN 21 Table II Blister Formation Induced by NH4-OH Exposure Site M.B.T. x B.F.T. 2 Volar Forearm 35 12.5 + 1.68 11.7 + 1.96 60 6.6 + 0.87 24.8 + 5.66 Upper Inner Arm 35 14.0 + 2.11 17.3 + 3.00 60 6.1 _+ 0.87 31.5 -+ 6.79 •Minimal Blistering Time, mean _+ S.E. in min. 2Blister filling Time, mean _+ S.E. in min. Table II also shows that in younger subjects, within 10 to 15 min after achieving an MBT, a tense blister appears. By contrast, Blister Filling Time is over 25 min for older subjects. Indeed, in two cases, the experiment was terminated at 90 minutes without obtaining a blister even though a follicular (MBT) pattern was evident. This suggests that integumental reactivity may be impaired in older subjects. To gain additional insight into this problem, a brief survey of integumental reactivity was conducted using a variety of excitants which when placed on the skin induce specific reactions, viz. erythema, wheals, vasodilation, stinging, etc. Preliminary findings reveal that in general older subjects as a group are less reactive (Figure 5). Such an age-related loss in the capacity to express certain inflammatory reactions has serious implications. For one thing, it means that certain clinical signs may be muted or missing entirely, making diagnosis of even common dermatological problems extremely difficult in older patients. Moreover, in various studies, e.g., allergic contact sensitization, the results may be meaningless unless it is reasonably certain that older panel members possess an adequate effector system for expressing the response. EXFOLIATIVE CYTOLOGY Since cells are continually being shed from the stratum corneum it becomes a simple matter to collect them for subsequent analysis (15). One method of collecting these corneocytes is by the sticky slide technique (16). In this procedure, a glass 3 x 1 slide coated with either tacky adhesive or double-sided scotch tape is pressed firmly on the skin surface to be examined. Upon removal, the specimen which retains the topographical relationships of the horny cells (corneocytes) can be stained for visualization. This method seems to be especially useful in studying the pattern of desquamation. Figure 6 shows sticky tape slides taken from the legs of a normal subject and one with dry skin. Note the appearance of large clumps in the dry skin preparation indicating that the corneocytes are shed as large aggregates rather than small clusters of individuals as is normal. Another method for examining the cytology of exfoliated cells is the detergent scrub technique (17). In this procedure, a glass well covering 3.8 cm 2 in area is held firmly to the skin. One ml of buffered 0.1% Triton X-100 © is added and the skin surface gently rubbed with a teflon scrubber for one minute. The resulting wash fluid which contains individual horny cells can then be processed in a variety of ways.

22 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Mean Grading Scores Age n t s 1 + 2+ 3+ DMSO HISTAMINE 48/80 ETHYL-N I COTI NATI CHLOROFORM-METHANOL LACTIC ACI ß I Figure 5. Integumental reactivity tests. Values represent mean grading from three independent observers. One extremely important parameter is the corneocyte count, the number of desquama- tion cells per square centimeter of skin surface. As such, it provides an indirect measure of epidermal proliferative activity since it is these cells which eventually migrate to the skin surface and are desquamated. In a previous study (18), age-related differences were determined in two groups: a) individuals with no history or signs of scalp disease and b) individuals with dandruff, a clinically noninflammatory hyperpro- liferative scaling disorder of the scalp. The results indicated that dandruff subjects had significantly higher corneocyte counts from the scalp than their corresponding age-matched controls. In fact, this elevated corneocyte count can be a very reliable way to assess the efficacy of various anti-dandruff medications (19). However, what is important to the investigative gerontologist is that in both groups, the older subjects had significantly lower corneocyte counts than the corresponding younger cohort. These results support the conclusion that with advancing age, the proliferative activity of the human epidermis is significantly reduced not only in normal individuals but also in those with a hyperproliferative disease such as dandruff (18). The detergent scrub technique also provides a simple method for the visualization of