HAIR GROWTH AND SHAVING MILDRED TROTTER Department of Anutomy, Washington University, Saint Louis ONE FIGURE INTRODUCTION I n an earlier paper observations were reported which indicated that the growth of hair on certain regions of the body is unaffected by shaving. Since the face was not one of the regions included, the present paper is a report of results obtained by shaving a selected part of the beard area. The beard more than any other part of the hairy covering of the body is commonly believed to be increased by shaving. These data are based on the length of the beard hairs shaved at stated intervals from a selected region of the face. My thanks are due t o the four meii who nillingly and faithfully carried out directions. MATERIAL Ah’D TECHNIQUE The region of the face from which the samples were taken was on the left cheek extending between two imaginary, horizontal and parallel lines; one at the level of the tragus of the ear, the other at the level of the lower margin of the lobule of the ear. Although the four men were of different physical ‘types,’ the adjustable conditions were kept as uniform as possible. I n lathering the face each man always used the same brand of shaving soap, and water of the same temperature. The razors were kept in as uniform a condition as possible; the three using safety razors used a new blade each time and the one using a straight razor made certain of its sharpness. These details are summarized in table 1. 373 374 MILDRED TROTTER TABLE 1 Cottditio?is of material and metJzod INDIVlDUAL A €3 C D COLOR OF HAIR COLOR OF EYES Black Medium brown Light brown Medium brown Dark brown Blue Blue Bro~m I AGE 20 25 21 24 I TEMPSRATURE 0% WATER 35°C. 40 'C. 41°C. 30°C. I KIND O F RAZOR U S E D Straight Safety Safety Safety The specimen was taken by using one downward stroke of the blade and with no stretching of the skin. It was then transferred from the blade to tissue-paper which was put into an envelope bearing the date and hour of the removal. The length of time elapsing between shaving and measuring the hairs was found t o make no difference in the length of the hairs ; that is, no shrinking or swelling of the hairs could be detected. Before measuring, the hairs were washed in a solution of ether-alcohol (equal parts of ether and 95 per cent alcohol) and distributed over a slide. The measurement was made with the aid of the ocular micrometer under lowpower magnification ( X 25). The hairs were found to be cut at an angle of about 45", and the measurement was made along the central axis of the hair shaft from extremity to extremity. I n every case one hundred hairs from each shaving were measured. The period of time over which the shavings were collected extended from the middle of January, 1927, to the middle of September, 1927. The mean temperature of the day (U. s. Weather Bureau Report) was plotted against the rates of growth, but no correlation was found. Table 2 shows the number of samples collected by each man and the length of time which had elapsed since the last shaving. To determine the number of hairs on which measurement for any particular period of growth is based, the number of samples indicated in the table should be multiplied by 100; thus, in determining the mean growth of hairs in a period of twenty-four hours since the last shaving for A, 1300 hairs were measured; for B, 1400 hairs; for C, 1700, and so on. Thus, a total of 25,400 hairs was measured. 375 HA41R GBOWTH AND SHAVING H O U R S BETWEEN S H A V I N G S mniVIDUAL TOTAL 12 24 36 48 60 72 84 96 13 14 17 19 13 0 0 0 6 0 19 14 2 10 0 2 23 12 20 20 8 D 1 0 0 0 0 0 0 10 0 13 18 76 36 69 73 Total 1 63 25 75 8 39 2 41 254 A B c MEAN GROWTH R A T E One of the earliest methods, and one still used to determine the growth of hair per unit of time, is that of dividing the length which the hair attains during a certain period by the number of units in the period and assuming that the result obtained is the mean growth per unit of time. The mean growth per hour was determined for each of the various periods which had elapsed since the previous shaving. As shown in table 3, there is quite markedly in the cases of B and C and to a slightly less degree in the cases of A and D a gradual decrease in the mean growth per hour, as more hours were allowed to elapse between shavings; in other words, apparently the longer the period over which the hair was permitted to grow the slower the mean increase in length of the hair. TABLE 3 S u m m a r y of the mean of the measurements HOURS BETWEEN SHAVINGS ME.4N A .0185 .0178 .0190 .0172 .0180 .0170 .0180 .0163 CROWTIi PER HOUR IN MM. B C D .0173 .0156 .0153 .0165 .0162 .0165 .0177 .0154 .0157 .0147 .0156 .0151 316 MILDRED TItOTTER These results are in accord with those of Seymour ( ’26), who measured shavings taken during parts of three years from tlie ‘zygomatic region of the face’ of one individual. He writes that “there is almost uniform decrease in the average rate as the hair is permitted to grow over longer periods,” and thus concludes that “the rate of hair growth is most rapid immediately subsequent t o cutting, the rate gradually lessening as the time of cutting becomes more remote. ’ ’ IIODAL GROWTH R A T E If tlie mean rate of growth per hour for each hair gradually decreases as tlie hair is allowed t o grow over longer and longer periods, the modal rate of growth f o r a unit of time ~vouldbe expected to decrease in a similar manner. For example, if, after a period of twenty-four hours since the last shaving, tlie modal growth (the length of hair appearing most frequently in the one hundred hairs of the various samples) was 4 mm., after a period of time twice that length, or forty-eight hours, the modal growth would be anticipated to be somewhat less than twice as much, that is somewhat less than 0.8 mm. However, in the graphs presented in figure 1 the modal growth of the hairs for the various periods of time which elapsed since the last shaving shows a consistent and direct relation to the length of the time periods. Thus, in C the four periods considered are of 24, 48, 72 and 96 hours since the last shaving and the modes are in 0.4 mm., 0.8 mm., 0.12 mm., and 0.16 mm. groups, respectively; B presents the periods with a twelve-hour difference, i.e., 24-, 3 6 , and 48hour periods, and with modes in 0.4 mm., 0.6 mm., and 0.8 mm. groups, respectively. A and D both present a longer series, and in an examination of the graphs one finds that here, too, the modal growths increase in direct proportion to the increase in the time period. This indicates that tlie majority of hairs showed a constant rate of growth f o r tlie periods eonsidered. H A I R GROWTH AND SHAVING 377 DISCUSSION There seems little doubt that the activity of the hair follicle is cyclic in character, including a growing period followed by a resting period. Exact measurement of the lengths of these periods has been made f o r follicles found in various Length M m . Fig. 1 Graphs showing in per cent the frequency of hair lengths recorded f o r the various time periods. The figures in the abscissae represent groups with a range of 0.2 mm., i.c., 0.2 mm. includes all lengths between 0.1 mm. aiid 0.3 mm.; 0.4 mm. includes all lengths between 0.3 mm. and 0.5 mm.; 0.6 mrn. include3 all lrngtlis hetwern 0.5 mm. and 0.7 mm., etc. 378 MILDRED TROTTER regions. Danforth ('25) has noted the cyclic activity of follicles producing terminal hairs on the ears and in the eyebrows; Bulliard ( '23) found a similar condition in hairs on the dorsum of the hand; and tlie writer ('23, '24) has reported for follicles of the leg, axillary, and pubic regions. The coiiclusion that hair on any particular region of the body does grow continuously seems to have little support, since every hair, showing individual and regional variation, of course, has an ultimate length. Hair of the head if uncut seldom reaches beyond the waist; and beards, except for a few freaks such as Dupr6 arid Duclos ('02) have reported, rarely grow longer than twelve inches. It is true that after an area is shaved one finds by close inspection that growth of hair is not apparent in all the follicles at once, nor after a few days do all the hairs have the same length in the follicles in which there is growth. Since all hairs are not in the same phase of the cycle at the same time, i.e., some are beginniiig growth, some concluding growth, and some in the resting phase, it may be suggested that it is by reason of this fact that the mean growth after shaving appears to be altered. For example, if an area of skin containing only six hair follicles were shaved, and after a period of twentyfour hours since that shaving each hair measured 0.4 mm., the mean and the mode would both be 0.4 mm.; if the same hairs were undisturbed f o r a period of forty-eight hours after shaving, and then five of them measured 0.8 mm. apiece, while the remaining one measured only 0.4 mm. (having in the meantime reached the end of its growth period), the mode would be 0.8 mm., but the mean would be reduced t o 0.73 mm. But, one could not infer from this that the length of time since the hairs were shaved has had anything t o do with their rate of growth. I n the light of what is now known of the cyclic nature of hair growth, the findings reported by Seymour and by the writer in this paper fail to supply evidence which indicates that shaving accelerates the rate of beard growth. On the contrary, the observations are entirely in accord with what would be expected on the assumption that shaving does not affect the rate of hair growth. + H A I R G R O W T H A N D SHAVING 379 CONCLUSIONS 1. No correlation was found between the variation in the day’s temperature and the variation in the hair growth. 2. The modal amount of hair growth increased in direct proportion to the increase in the time period. 3. The mean amount of hair growth decreased per unit of time as the time period increased, but this may be explained as due t o the cyclic activity of the follicle, since the longer the period the greater the number of follicles to become quiescent. 4. There was no evidence that shaving liad any effect on the growth of the beard. LITERATUlZE C I T E D BULLIARD, H. 1923 Influeiice de la section et du rasage repete sur l’evolution du poi]. Annales de Dermatologie et de Syphiligraphie, V I Series, T. 4, no. 6, pp. 386-391. DANFORTH, c. H . 1925 Hair with special rcfcrence to hgpertrichosis. American Medical Association, Chicago. D U P R ET ~ DUPLOS 1902 La barhe chez les ali6n6s. S T Congrhs des a l i h i s t e s rt iieurologistes franpais. (Reviewed in Ann. Dermat. and Syphilig., T. 3.) SEYMOUR, RAYMOND J. 1926 The effect of cutting upon the rate of hair growth. American Journal of Physiology, kol. 78, no. 2. TROTTER, MILDRED 1923 The resistance of hair to certain supposed growth stimulants. Archives of Dermatology and Syphilology, vol. 7, pp. 93-98. 1924 The life cycles of hair in selected regions of the body. American Journal of Physical Anthropology, rol. 7, no. 4, pp. 427-437.