Vol. 55, No. 3 INVESTIGATIVE DERMATOLOGY THE JoURNAL OF Printed in U.S.A. Copyright@ 1970 by The Williams & Wilkins Co.

SHAVING AND HAIR GROWTH*

YELVA L. LYNFIELD, M.D. AND PETER MACWILLIAMS, M.D.

ABSTRACT The effect of repeated shaving on human hair growth was studied. Five healthy young white men each shaved one leg weekly for several months and left the other leg as a control. No significant differences in total weight of hair produced in a measured area, or in width or rate of growth of individual hairs, could be ascribed to shaving.

Dermatologi ts and dermatology textbooks firmed Trotter's work by performing a differential The black hairs on his legs acrree that shaving has no effect on hair growth hair count on one man. bleached,t permitted to grow for two weeks, portion of were (1-3). Since the actively growing shaved, and examined for pigmented proximal hair the hair, the root, i · located in the deep dermis shafts which indicated growth since bleaching. or subcutaneou fat, procedures directed only Hairs which were completely blond after two weeks at the fully keratinized, metabolically inactive were counted as telogen. On his left leg, 69% of hairs were telogen; on his right leg, 67% of 90 hair shaft above the skin surface theoretically 142 hairs were telogen. hould not influence growth. The basis for the Five men had the hair on their legs shaved with textbook tatements consists of shaving ex­ a straight razor and warm water. The first shavings P riments performed on humans in the 1920's were discarded. One to three weeks later, a care­ and ( 4-6). Although careful and painstaking, they fully measured area on each leg was shaved shavings collected. A 10 by 10 em square of increase in length all the m a ured only the rate card was placed just below the patella, with its of individual hair shafts. upper edge horizontal and centered over the patel­ Recent experiments on guinea pigs (7) and lar tendon. The card was outlined with Micropore mice ( ) showed that clipping stimulates hair tape and then removed. All the hair within the 10 outlined by tape was shaved and growth in the"'e species, by inducing anagen by 10 em area ected by gentle brushing into a weighing dish. An at­ coll prematurely in telogen hair follicles. It was dried in a desiccator with calcium chloride tempt to determine whether this occurs in overnight. and then weighed on an analytic men is reported here. The effect of repeated balance. The length and width of 10 dried hairs ocular shaving on the total amount of hair produced from each ample was measured with an standardized against a Neubauer . of skin was investigated. This wa micrometer on an area counting chamber. For several months thereafter measured by weight, which depends on the each man shaved one leg weekly, discarding the number of anagen hair a well as the lenoth1:> shavings, but did not shave the other leg. Then and width of individual hairs. The effect of samples from both legs were again carefully col­ intervals as in the repeated shaving on the rate of growth and lected. shaving at the same collection, and examining the hair in hairs was also mea - previous diru:neter of individual identical fashion. ured. vVhile accuracy in measurement was enhanced by increasing the time during which the samples MATERIALS A D METHODS were permitted to grow, the length of the collec­ tion interval was limited by the possibility that subjects were h alth:v white men in their The the first shaving might stimulate anagen. If 20's. The anterior crural area wa selected for study Saitoh's (10) estimate of three weeks as the time b cause of its high proportion of telogen hairs and required for new hairs to emerge to the surface is relatively long duration of telogen. This would accepted. the hairs collected by the second shaving make it easier to detect premature onset of anagen should include only hairs which were already in han on an area with a low proportion of telogen anagen at the time of the first shaving, one to three hairs and a short telogen duration relative to ·weeks preYiously. n.nagen, such a the alp. According to Trotter (9). 83 %) are in telogen, and mo t l g hairs (average RE ULTS stay in telo en much longer than anagen. We con- gives details of the having per­ Received Mar h 20. 1970; accepted for publica­ Table I tion April10 1970. formed on the five subjects. Table II reports *From the Dermatology Section. Medical erv­ ic . Brooklyn Veterans Administration Hospital, t The bleach used was Born Blonde supplierl Brookl n, New "York 11209. by Dr. B. M. Lanman of Clairol Inc. 170 SHAVING AND HAIR GROWTH 171

TABLE I shaved and a symmetrical area left unshaved can be ascribed to the shaving. Duration of Days of growth Subject Age study, weeks of shaved The weight of hair produced on a constant specimens area of skin over a given time interval de­ pends on the number of growing hairs (% z 26 19 22 anagen x number of follicles), and the diam­ F 27 9 8 M 23 16 14 eter, density, and rate of growth (increase s 24 15 14 in length) of each hair. This may be expressed v 24 16 8 by the formula: W == KAND2 dL the measurements of the samples. Each value where: for width and length of hair reported is the W is weight of hair produced: K is con­ median of ten hairs measured after random stant; A is ratio of anagen hairs to total selection from the collected sample. The dif­ hairs; N is number of follicles in area; D Is ferences between initial and final measurements diameter of hair; d is density of hair; L is do not appear significant at first glance nor rate of increase in length. when analyzed statistically by paired t-test Assuming that N, D, d, and L remain (p > .05). constant, W varies only with A. The data No significant differences in rate of hair sho·wed no significant change in D and L, and growth, either in length or weight, and no there was no reason to suspect a change in coa rsening of individual hairs, could be as­ D or d. l\!Ieasurement of W showed no signifi­ cribed to shaving. cant variation and, therefore, A, the propor­ tion of hairs in anagen, was not changed by DISCUSSION shaving. Hair growth is influenced by many factors, If W had changed significantly in this ex­ such as temperature (10) and nutrition (11). perin1ent, the next step was to count the hairs These factors influence both legs, and dif­ in each sample, which were all the anagen ferences between a crural area repeatedly hairR and only the anagen hair:::: in each 100

TABLE II

Hair width ,urn j Hair growth mm/ day Hair growth mg/ day Subject & leg Initial Final Dif Initial Final Dif Initial Final Dif I (Z) Test 54 51 -3 .25 .23 - .02 .32 .72 + .40 Control 59 58 -1 .26 .24 -.02 .43 .5G +.13

(F) Test 80 80 0 .31 .30 - .01 1.11 .66 -.45 Control 80 72 -8 .35 .32 -.03 1.30 1.02 -.28

(M) Test 51 61 +10 .31 .29 -.02 .38 .54 +.16 Control 56 65 +9 .28 .30 + .02 .32 .58 +.26

(S) Test 49 59 +10 .28 .29 +.01 .62 . 6 +.24 Control 56 53 -3 .27 .24 - .03 .48 .66 +.18

(V) Test 70 59 -11 .24 .30 +.06 .44 .61 +.17 Control 78 43 -35 .26 .30 +.04 .44 .61 +.17 172 THE JOURNAL OF I NVESTIGATIVE DERMATOLOGY sq em crural area studied. An increase in 2. Andrews, G. C. and Domonkos, A. N.: Diseases of the Skin. Saunders, Philadelphia, 1963. number of anagen hairs could have been 3. Rook, A., Wilkinson, D . S. and Ebling, F. J. demonstrated directly. However, since the G.: T extbook of Dermatology. F. A. Davis Co., Philadelphia, 1968. weight of the amples did not change with 4. Trotter, M.: H air growth and shaving. Anat. shaving, the task of counting hairs lost its Rec., 37: 373, 1928. importance. 5. Trotter, M.: The resistance of hair to certain supposed growth stimulants. Arch. Derm., 7: This experiment gave additional evidence 93 , 1923. that shaving does not make hair grow faster 6. Bulliard, H. : Influence de la section et du rasage repete sur !'evolution du poil. Ann. or stimulate new hairs to grow. This is ac­ Derm. Syph., 4: 386, 1923 . cepted in the English literature, but Japanese 7. Kim, J . H., Herrmann, F. and Sulzberger, M.: Effect of plucking and of clipping on the studies quoted by Saitoh ( 12) disagree. Saitoh's growth of hair in guinea-pigs. J. Invest. own measurements of individual chest hairs Derm .. 38 : 351 , 1962. shaved twice at weekly intervals showed no 8. Borum, K.: Influence of clipping and chemical epilation on hair growth in mice. Acta Path. effect on growth rate. Microbial. Scand., 43: 127, 1958. AlthouO'h, strictly speaking, our data ob­ 9. Trotter, M .: Life cycles of hair in selected regions of the body. Amer. J . Phys. Anthrop., tained from young men's legs should be ap-:­ 7: 427, 1924. plied only to trou er-covered, seldom-noticed 10. Saitoh, M., Uzaka, M. and Sakamoto, M.: Human hair cycle. J. Invest. Derm., 54: crural skin, the conclusions may reassure 65, 1970. those b auty-conscious ·women who shave their 11. Ryder. M. L.: Nutribonal factors influencing legs, their axillae, and even their faces. hair and wool growth, Chap. 14, Biology of Hair Growth. Eds., Montagna, W. and Ellis, R., Academic Press, New York, 1958. REFERENCES 12. Saitoh, M., Uzaka, M. and Sakamota, M. : Rate of hair growth, Chap. 14, Advances in 1. Pillsbury, D. M., Shelley. W. B. and Kligman, Biology of Skin, Vol. IX. Eds., Montagna, A.M.: Dermatology. Saunders, Philadelphia W. and Dobson, R. L., P ergamon Press, 1956. ' New York, 1969.