CHANGES IN CHINESE HAIR
GROWTH ALONG A FULL YEAR
C. Liu*, J. Yang*, L. Qu*, M. Gu*, Y. Liu*,
J. Gao*, C. Collaudin† and G. Loussouarn†
*L’Oreal R & I, Jinyu Rd No. 550, Shanghai, 201206, China
and †L’Or_eal R & I, 20120611-13 rue Dora Maar,
Saint-Ouen, 93400, France
INTRODUCTION
ABSTRACT
As a physical fibre, the human hair shows a large diversity in shape, colour, length, diameter, ellipticity. . .with ethnics, age or fashion. As a biological end
product of the hair follicle ‘machinery’, it obeys to successive cycles of growth, arrest, shedding and a further regrowth. Aim of the study was to confirm the
existence of seasonal hair growth cycle among Chinese subjects and objectivize the seasonal effect of hair loss.
METHODS
1
Protocol
At approximately comparable days within months, subjects came into the laboratories for a consecutive 2-day presence (D0 and D2) of about an hour
each, due to the inherent practical aspects of the widely used phototrichogram technique. Visits were repeated monthly over a 1-year period.
2
The phototrichogram technique
At D0, a small scalp area (1.5 cm by 1 cm) of the vertex region was shaved. A first photograph was then immediately taken under standardized lighting
conditions.
The Canfield Epiflash objective, mounted on a Nikon D90, allows being gently pressed onto the scalp area. Therefore recording pictures at a constant
distance between scalp and camera for all subjects. The same procedure was repeated 2 days later (D2).
3
Image analysis
For each month and subject, these two consecutive digital photographs were processed through image analysis, using an L’Oreal dedicated software.
Globally, the latter allows a precise reframing of the two pictures, an automatic detection, counting all hairs and comparing the lengths of individual hairs.
This procedure allows, at D2, hairs of a longer size at D2 (anagen, growth) or of a same length (telogen, no growth) to be detected and counted. These
rapid computations provide the total number of hairs, within the same recording frame, their density (N/cm2), A% (total grown hairs/N) and T% (total not
grown hairs/N). Growth rate comes as a logical step, by calculating the individual difference in length over a 2-day period of anagen hairs. Lastly, a manual
procedure allows the diameter of a given hair to be recorded by selecting two regions along its shaft, leading to an average width (in lm) from an automatic
calibration referred here as its ‘diameter’.
RESULTS
1
Global data
Table below summarizes the ranges of major hair growth
parameters of Chinese subjects observed during 13 successive
months, the values of which clearly correspond to healthy head of
hair, free from alopecia.
2
Changes in telogen values, anagen values, growth
rates, hair density and diameter over a one-year period
With regard to T%, Fig. (a) below illustrates the average changes in T% along a full
year for Chinese subjects, indicating a higher value in September, as compared to
other months. Whereas, Fig. (b) illustrates the average changes in A% along a full
year, indicating a lower value in September.
Below illustrate a rather constant value of hair growth rate (375–425 lm/day range)
along the year.
3
Relation between growth rates and diameters
As all analysed hairs were not individually identified by these two
criteria (diameters being determined at random), classes of diameter
were created (70–80 lm, 80–90 lm etc. . .) allowing to calculate, for
each class, an average growth rate being calculated. Figure below
illustrates, both genders included, a linear and highly significant
correlation between both parameters, that is the thicker the hair, the
faster growing. This confirms previous data obtained on
individualized Asian (straight shaped) hairs.
With regard to hair density (below figure), Chinese women present slightly higher
values than men by about 10 hairs/cm2 (approx. 225 vs. 215, respectively). However,
hair density of both genders do not show significant changes along the year, the
average monthly values oscillating around 220/cm2.
Gender effect on hair density for Chinese population
240
Hair density (Hair cm-2)
235
230
225
220
215
210
205
Male
200
Female
195
Jan
Feb Mar Apr May Jun
Jul
Aug Sept Oct Nov Dec
Jan
Month (2012-2013)
CONCLUSION
The data collected monthly over a full year globally confirm the existence
of a seasonal hair growth cycle (increased T% at late summer) among
Chinese subjects. As compared to other ethnics, Chinese hairs appear
thicker and of a faster growth, which is in agreement with previous
findings. In addition, this data confirm the strong link between hair growth
and hair thickness by analysing about 1600 individualized straight hairs
from Asian subjects.
With regard to hair diameter, below show rather constant average values along the full
year.