222 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Fiber and Site Count on Left Side of Head Number of Fibers/ Number of Sites/ Average Number of Fibers/ Subject Age cm 2 cm 2 Site 1 59 a 95 48 2.0 2 48 a 131 58 2.3 3 29 145 67 2.2 4 37 153 86 18 5 47 • 159 64 2.5 6 30 195 72 2.7 7 36 196 84 2.3 8 36 205 76 2.7 9 27 206 88 2.3 10 42 208 105 2,0 11 24 227 87 2.6 12 26 231 88 2.6 13 33 233 82 2,8 14 42 243 110 2.2 15 31 245 98 2.5 16 31 250 110 2.3 17 31 251 108 2.3 18 36 275 101 2.7 19 37 279 98 2.8 20 28 295 90 3.3 Average b 35.5 211 86 2.4 Average c 32.7 226 91 2,5 •These subjects were Chinese, all others apparently Caucasians. bAyerage for the 20 subjects. CAverage for the 17 Caucasian subjects. the participants were between 24 and 42. If the 3 oldest individuals are left out, the correlation between age and hair count approaches zero, indicating that this age group is rather homogeneous, or at least the individual variability--probably due to inherited factors-•is a stronger parameter than age for this sample size. The values of the average fiber count/cm'--211 and 226---are noteworthy in the respect that they are practically identical with those given by Barman (10, 11, 13, 15, 16), although, different from some others cited by Giacometti (22). A full head of adult hair is commonly stated to contain about 100,000 (3, 5) to about 120,000 (4) fibers. According to Behrman (23), the average scalp area for an adult is in the range of 775 cm =. Using this figure, the fiber density would only be 129 fibers/cm = for a 100,000 fiber adult head of hair. Only 1 individual in our panel was below this number. With the presently obtained fiber densities of 211 and 226 fibers/cm •, the full head of hair should comprise 164,000 and 175,000 fibers, respectively. Although the densities were determined only at a specific site on all heads, this site is neither an outstandingly dense hair growth area nor are the d'ifferences among different scalp areas very large on adult heads (13, 14, 15). Therefore, we believe the estimate for the average fiber content of a full head of hair should be raised to the 160,000 to 180,000 range for women in the age group of 25 to 50. The commonly used low figures probably originate from the works of Stelwagon and Pinkus (24) quoted and even misquoted later (25, 26).

FEMALE SCALP Table II Fiber and Site Count on Right Side of Head 223 Number of Fibers/ Number of Sites/ Average Number of Fibers/ Subject cm 2 cm 2 Site 2 175 68 2.6 3 169 83 2.O 4 142 81 1.7 10 270 105 2,6 12 208 73 2.8 14 182 83 2.2 15 239 ,100 2.4 18 203 70 2.9 Average 199 85 2.4 Average a 204 89 2.3 alert side of head for same group of subjects, derived from values in Table I. • Hair is known to grow in groups on the skin of lower mammals (27), primates (28), and on certain body areas of man (20, 21, 22, 29, 30) including the scalp. Within the site of such groups, each fiber is at most a few diameters away from its neighbors, while the sites are well separated from each other. The site count, obtained together with the fiber count, is shown in Table I. It is seen that the site count ranges from about 50 to just over 100 per cm 2. Based on the average values, the centerpoints of such sites are more than 1 mm distant from their neighbors. The average number of fibers per site ranges from 1.8 to 3.3, but 90 per cent of the participants were between 2 and 3. The number of sites showed a reasonably good positive correlation (0.800) with the total ß : number of fibers. However, the correlation with age was even weaker (-0.518) than that of the total number of fibers. The results of a second measurement on the right :.: side of the head of 8 individuals are given in Table II. It is seen that sizeable differences can exist in both fiber and site count on the 2 sides of the head, even though they were symmetrically positioned. The variation is randomw neither side is preferred--as is shown by the close correspondence of the averages for the two sides. These facts indicate that, while single counting for a panel is probably satisfactory, it may be misleading for any one individual. FIBER DISTRIBUTION BY GROUP SIZE The term "group" is used here to describe 2 or more fibers within a single site, whether they are separated by stratum corneum (simple fibers) or issue from a common follicle orifice (compound fiber) or contain a mixture of the 2 forms. The average number of fibers in a group varied between 1.8 and 3.3 for our panelists, as shown in Table I. The actual distribution of the fibers according to group size varied widely among the indi- viduals. The results are given in Table III. The proportion of single fibers ranged from 1 to 23 per cent within the panel of 20. On some subjects, the largest groups contained only 4 fibers while on others 8. Even an identical maximum group size--as seen on sub- jects 1, 4, 5 and 17--does not ensure a similar distribution curve within the range. On the average, two-thirds of all fibers were in groups of 2 and 3, slightly more in the latter category. When the group frequency is expressed as a function of size, the results