HUMAN SKIN SURFACE LIPIDS 91 GRAPH I REGIONAL DIFFERENCES AND SEASONAL VARIATION OF ACID .NUMBER (MEDIAN VALUES) 50 40 -L•* * *•. 42 40 38 "•,• 44 38 4655 / .•.•60__.__.• • 49 55 7171 • •7272 UPPER FIGURES: Medians of Acid Number for all •t Assays. LOWER LEFT: Medians for Nov. - April Temp. (oF) _ Median: 41 Range: 4 - 74 LOWER RIGHT: Medians for May - •t. Temp. (oF) _ Median: 69 Range: 33 - 90 70 ! 50 6 57 64 55 66 67 68 65 56 64 56 66 57 56 75 56 75 80 89 75 84 Subject and Test Sites. Forty-five healthy volunteers, twenty-two to thirty-eight years of age were subjected to the examinations. Thirty- seven of these were males, 35 white, 2 Negro and eight were females, 5 white, 2 Negro, 1 Chinese. Most of the subjects were investigated on several occasions and whenever feasible, both during the warm and cold seasons of the year. The same [21] skin areas were used for collecting the lipid samples which were standard test sites also in our previous studies (1, 2, 3, 6, 7). The sites are identified on tables as well as Graphs I and II. Similarly, the precautions employed prior to testing, avoidance of washing of the sites for at least forty-eight hours, etc., were identical with those described previously (1, 2, 3, 6, 7). In all, 1214 A.N. assays have been performed to date. RESULTS Upon the advice of our biostatistician* the results are presented as medians, rather than as mean values, since the median--representing the * Dr. R. R. Freudenthal, Statistical Consultant, Jackson Heights, N.Y., evaluated our re- sults mathematically and statistically.

92 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS