QUANTITATIVE ASPECTS OF CORNEOCYTES 5 We choose 2,500 RPM for technical limitations of the turbine. Figure 4 shows the effect of increasing time at two fixed speeds. At 350 RPM, numeration increases slowly up to 120 sec., reaching the 12,500 cells/cm 2 obtained at 2,500 RPM with this female subject (no. 13 in Table I). For a higher level of desquamation (male subject no. 1 in Table I), plateau is reached in less than 30 sec. Rotating time can be limited to 30 sec, but one minute was generally found more reproducible. CELL COUNT The cell count (Table I) shows large variations from subject to subject (1,570 to 34,500 cells/cm2). Compared to the techniques used by Marks et al (6) on the same body site, the turbine machine gives corneocyte counts between those obtained with the passive method (1,000 to 2,000) and the scrub apparatus (90,000 to 130,000), assuming a mean count of 10,000 corneocytes/cm 2 in the population studied here. This amount, and the fact that our apparatus avoid mechanical stress on the skin surface, would afford a good approach of the natural desquamation. In practice, if no precaution occurs, measured desquamation depends on daily habits (time between last bath and measurements, washing frequencies, use of cosmetics, nature of soap or shampoos), on clothes-skin relationships, on efficacy of the detergent solution in regard to the greasiness of the skin (unpublished results). So, these data may integrate such factors which influence cell counts. Furthermore, larger intersubject variations are observed in humans than in animals. In hairless mice, for example, the number of cells varies from 1,500 to 3,500/cm 2. Finally, natural desquamation should be apprehended by taking into account such factors which influence the results. QUALITY OF CELLS Quantimet can separate three classes of features: "Normal" corneocytes will be the basis for surface area measurements. They represent 70% of total features in the suspension. Shape and number are a pattern of each subject and body site, variations being due to local or environmental changes. Broken cells represent about 10% and would reflect the influence of mechanical or chemical stress on the corneocyte integrity. The results reported in Table I do not correspond to a relative amount of aggregates but to the total amount of corneocytes implied into aggregates. No information is given on the basic number of cells in each aggregate. These would provide an estimate of horizontal cohesiveness between corneocytes compared to vertical cohesiveness. To complete knowledge on the quality of harvested features, studies are undertaken to classify with Quantimet abnormal cells like nucleated parakeratic cells or irregularly shaped corneocytes. Such classification will be the basis for monitoring the response to therapy: the proportion of nucleated cells, for example, should be an indication of the evolution of a lesion. SURFACE AREA OF CORNEOCYTES Quantimet gives measurements of the so-called "projected area" of corneocytes (5). A resulting mean surface area of 860 _ 25/•m = in the population studied here, is in good

6 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS agreement with previously published data for the same body site (3). To each subject, Quantimet provides accuracy at low magnification for area measurements on more than one thousand of "normal" corneocytes. Interest takes place in studies on phenomena like aging, seasonal variations, sun expositions, effect of cytostatic drugs. If local stress can immediately modify desquamation, size modification would appear after a deeper injury and consequently with a minimal transit time of 20 days (9). CORRELATION Correlation between manual counting and computer calculation is illustrated by Fig- ure 5. Quantimet count x10 4 Manual count x 0 • ' • 0 I 2 4 Figure 5. Correlation between automatic counting and manual counting. Results are expressed as the number of corneocytes extracted per cm 2 of skin surface. A correlation higher than 0.99 on twenty measurements is obtained, the Quantimet giving a constant 5% higher value than the manual estimation. We cannot give any definitive explanation for this difference but we dotice that the human eye has some difficulty in correct estimation of the number of cells in an aggregate. CONCLUSION Because of its high resolution, Quantimet needs low magnification for corneocyte counting, surface area measurements and classification of cells. In addition, these parameters are known simultaneously in a very short time.