Hair is considered as an annex of skin, made of keratin. Colour, thickness or apperance may be different; hair is an image of our culture or our origins and also our tastes. On average, hair comprises 120000 to 150000 hair which grow constantly throughout our life …
Hair , general data …
H
air
has
a
diameter
of
50 to 100
micrometers
(a millimiter, i.e. 1,000 micrometers, is then equivalent to
10 to
20 hair's diameter
)
.
Their
growth
is slow
:
the guess is
that
hair
grows
about
1
cm per
month
,
and
one loses
from 50 to
100 hair every day
.
Depending on the ethnic origin
,
hair texture
may
be
different
:
crisp
, thin
, straight
or
curly
. This
depends on
the implantation of
hair
follicles
.
For
example
,
straight
follicles
give a very
stiff
hair
as for people from Asia,
while
more
supple
follicles
provide
a
wavy or
curly
hair
.
Further, there is
a
wide
range
of
colours
from a
very light blonde
to
dark brown
. As for
skin
or eyes
,
hair colour
is due
to
the
well-known
melanin
which gives
the
hair
fiber
its colour.
Structure of the hair follicle and hair
The
hair follicle
(
the hair
entire
structure
)
works after a cycle, which makes new hair on a regular basis.
This
follicle
comprises different parts:
•
The
hair
implanted
into the
hair follicle.
•
The
sebaceous
gland
opened to
the
hair
canal
.
Each
hair follicle
is
connected
to
a
sebaceous
gland
;
hair
and
sebum
follow the same way
to
reach
the
outer
skin
.
•
The
piloerectile muscle
,
a
muscle at
the bottom of
every
hair
.
It is active in the
thermoregulation process,
through
reflex
goosebumps
.
Hair comprises
a
visible part
called
the
hair shaft
and
a
deep end
:
the root
.
Hair growth
Hair bulb
is the birth place.
Due to
cells divisions
, hair
springs
, then grows up and up to
the
surface of
skin
.
Hair growth
goes in
three
stages
:
•
The
anagen stage
: cells multiply, allowing for the growing of hair.
This
phase
is
also when
the
synthesis
of melanin
is
at its highest rate,
giving
hair its colour.
•
The
catagen
stage
is
a
resting phase
;
cells division
s
and
synthesis
of melanin
end
.
•
The
telogen stage
is
the
phase
of getting rid of the "dead hair", which
eventually
fall
s down by itself.
Thus,
along our life
,
hair follows
a cycle
of
continuous
growth
:
when
hair
dies
,
a new one is given life in the hair bulb.
Hair and Cosmetics
H air, as we call it, or better, hair shaft ( the visible part ) is biologically dead . However , it acts as a " blot " absorbing materials applied on it. Cosmetic products used on hair sheathe hair and improve its aspect, without any true action as the fiber is biologically inert.
