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Hair growth and shaving.

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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.
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