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COSMETIC
Hair
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What
is hair?
Hair is a characteristic skin appendage found only in mammals whose
function was basically meant to provide insulation, but with evolution
it has lost most of its protective function and instead plays an
important role in social interactions.
How many
hairs does a human head have?
A human head has anywhere between 100,000 and 150,000 hairs. Oriental
heads have most hairs and redheads have the least. Apart from the palms
and soles almost all skin has follicles. But not all hair grows to the
same length or at the same rate.
What is a hair follicle?
Hair follicle is stocking like in growth of the skin epithelium which
manufactures and anchors the hair to the skin
How does
a hair follicle develop?
In humans, follicle formation begins on the head in the fourth fetal
month of gestation, and then moves downward to the remainder of the
body. Follicles first produce soft, short and fine hairs, which are
called “lanugo” hairs.
What are
the different parts of the hair follicle?
The follicles are slanted in epidermis and an oblique muscle the
arrector pili runs from the middle of the follicle wall to the dermo
epidermal junction, additionally one or more sebaceous glands open into
the follicle.The follicle may be divided into vertical components :
Infundibulum, Isthumus, Suprabulbar region and Bulb
What is
the composition of hair?
The hair as we see it is a compact structure made up of dead cells.
Individual hairs are composed chiefly of the horny scleroprotein known
as keratin and contain neither blood vessels nor nerves. They usually
contain pigment (except in the case of albinos). The shaft of the hair
consists of modified epithelial cells arranged in columns (cortex)
surrounding a central medulla (or core) and covered with thin, flat
scales (cuticle).
What is the density of hair on scalp?
Accurate quantitative analysis of scalp hair density is difficult and
time consuming.
Scalp possesses the greatest density of hair fibers 300 –
500/cm2(different figures are quoted by different specialists ranging
from 130-280/sqcm2), Chest about 100/cm2, Thigh about 50/cm2.
 How
does hair grow?
The hair follicle bulb is like a minute factory which manufactures
cells continuously. As new cells are formed the older ones are pushed
into the follicle towards the surface. The cells on reaching a
particular point undergo cell death and are converted into a
scleroprotein called keratin, which is then compacted to form the hair.
This continuous activity is responsible for the hair growth.
During anagen the follicle actively grows hair.
During catagen the follicle is almost entirely
degraded.
During telogen the follicle rests prior to
re-initiation of an anagen phase and the growth of a new hair shaft. On
any given day, human beings lose about 50-100 scalp hairs due to
exogen, these are the hairs we find in our comb, brush and shower
drain. Shedding in excess of this may be due to an increase
in the follicles of scalp hair in the telogen stage and should be
addressed to contain hair loss.
At any given time approximately 90%of our scalp hair are in the growing
phase and about 10% in the resting phase, if the scalp is healthy and
not affected by any condition that causes hair loss.
Recently a fourth phase has been added based on the findings in
patients of pattern hair loss. This is known as the Kenogen or the lag
phase. This is the period after the hair has been shed and before the
new hair formation begins. It is this phase that is prolonged in
patients of Pattern Hair Loss
The normal growth rate of scalp hair is 0.3- 0.4 mm per day or roughly
1cm per month. Hair growth has a cyclical pattern that can be affected
by a number of genetic, disease, medication or other factors to cause
hair loss.
 Why do some people have very long
hair? How long can your scalp hair grow?
If you do not cut your hair then you can grow it quite long, but there
is an upper limit to the maximum length that you can grow your scalp
hair.
There are various papers that examine the time duration for scalp hair
follicles are actively producing a hair fiber. The most frequently
quoted time period is 1000 days(2-6 YEARS), but this figure is a rough
approximation. The time duration of anagen growth, plus knowing what
length of hair fiber a scalp hair follicle can produce per day, will
enable a calculation of the average maximum length that scalp hair can
grow to. Research on humans suggests that active hair fiber growth
production from scalp hair follicles may last from 500 to 1800 days.
The scalp hair fiber growth rate is between 0.3 to 0.4mm a day. For the
most part, the studies were done with male volunteers, but a few other
studies indicate similar results for women too.
If you put it all together in a calculation, the research would suggest
that the maximum length scalp hair can grow to, is between 20 and 60
centimeters. However, from the picture below you can see that some
people are able to grow their hair much longer. The upper limit to
scalp hair length is determined by our genes. Some people have genes
for short hair, others grow hair much longer.
How is hair growth regulated?
The hormones called androgens are important control factors in hair
growth and in inherited male and female patterns of hair loss. The
androgen hormone testosterone and its metabolite dihydrotestosterone
(DHT) are the key control factors:
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Testosterone
is a key control factor in the growth of beard, underarm and pubic hair.
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Scalp
hair loss is associated with presence of DHT in male and female pattern
hair loss. DHT plus the presence and activity of hair loss gene(s) are
the key factors underlying male and female pattern hair loss.
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The
androgens mediate their effect by binding to the androgen receptors
present in the follicle. The testosterone is converted to DHT by the
action of the enzyme 5-Alpha reductase. The DHT then binds to
the receptor and initiates its action
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