STINGING CAPACITY OF APPLIED SUBSTANCES 209 time to time for retention of sensitivity to lactic acid. Susceptibility returns after a rest period of several weeks. We have recently developed a simpler method of selecting stingers for recruitment of test panels. Thermally induced sweating is not required. The application of 10 per cent lactic acid to the face will elicit stinging which is almost equivalent to 5 per cent acid on sweating skin. The same is true for 15 per cent ethanolic ADP. These higher concentrations have no effect on nonstingers. Let it be clearly noted, however, that tests of unknown materials must be carried out on sweating facial skin of preselected stingers. It should also be noted that substances with a high capacity to induce stinging can do so in the absence of sweating. REFERENCES (1) W. W. Wilson, R. Quero, and K. J. Masters, The search for a practical sunscreen, South. Med. J., 59, 1425-30 (1966). (2) J. A. Parrish, M. A. Pathak, and T. B. Fitzpatrick, Facial irritation due to sunscreen products, Letter to the Editor, Arch. Derrnatol., 111,525 (1975). (3) D. R. Armstrong, M. L. Dry, C. A. Keele, and J. W. Markham, Methods for studying chemical excitants of cutaneous pain in man, J. Physiol., 115, 59P (1951). (4) K. Laden, Studies on irritancy and stinging potential, J. Soc. Cosmet. Chera., 24, 385-93 (1973). (5) R. W. Shanahah and C. O. Ward, An animal model for estimating the relative sting potential of sham- .poos, J. Soc. Cosmet. Chern., 26, 581-92 (1975). :: (6) D. A. Weigand and M. M. Mershon, The cutaneous irritant reaction to agent 0-chlorobenzylidene malo- nonitrile (CS). II. Quantitation and racial influence in human subjects, Edgewood Arsenal Technique No. 4332, 1970. (7) D. A. Weigand, C. Haygood, and J. R. Gaylord, Cell layers and density of Negro and Caucasian stratum comeurn, J. Invest. Dermatol., 62,563-68 (1974).

j. Soc. Cosmet. Chem., 28, 219-229 (May 1977) Observations on female scalp hair population, distribution, and diameter ELLYN M. COTTINGTON, ROY H. KISSINGER, and WILLIAM S. TOLGYES I Gillette Research Institute, 1413 Research Boulevard, Rockw'lle, MD 20850. Received July 20, 1976. Presented Ninth IFSCC Congress, June 1976, Boston, MA. Synopsis : :. :. SCALP FIBER POPULATION DENSITY, GROUPING, and DIAMETER were studied on a panel of 20 : women ranging in age from 24 to 59. The average number of fibers per square cm was above 200, which can " be translated to about 170,000 fibers for a full head of hair. The fibers grow in a variety of groupings with :i.:: wide individual variations. The average fiber diameter for the group was about 70 •m, with individuals rang- ing from under 60 to about 90 •m. The influence of the fiber number and diameter on the bulky appearance of the hair is often masked by other characteristics such as waviness and hair care practices. INTRODUCTION The hair fiber characteristics which determine most cosmetically important hair mass mechanical behavior are: population density, diameter, moduli, shape, and fiber-fiber interactions (1). Fiber length, not being an intrinsic characteristic, is excluded from this list, even though it influences certain properties such as combing (2). Most cosmetic products and processes perform their functions with regard to hair mass mechanical be- havior in the dry state by modifying the last 2 groups of parameters. The first 3 groups of parameters, even if partly or completely outside the influence of cosmetic products, are of interest to the cosmetic industry because of their influence on hair behavior. This paper is aimed at collecting and interpreting data on scalp fiber population and diameter of adult women. The traditionally accepted value for the fiber population of a full head of adult hair is about 100,000 (3, 4, 5). The mean fiber diameters for groups of individuals range from 60 to 100/zm (6, 7, 8, 9) with individual fiber values from 25 to above 100/xm hav- ing been reported (10, 11, 12, 13, 14, 15, 16). We wanted to check the validity of the accepted mean values, investigate variations between individuals, establish ranges of values for single heads, and determine correlations, if any existed, among different characteristics. 219