Hair structure and hair growth cycle

1. Hair Structure, Hair Growth Cycle,
Dr. Nilesh S. Kulkarni
Associate Professor in Pharmaceutics,
PES Modern college of Pharmacy (For Ladies),
Moshi, Pune 412105.

2. Hair Shape
Can be straight, curly, or kinky, depending on the cross-section, which may
be round, oval, or crescent-shaped.
Round
(Straight)
Oval
(Curly)
Crescent moon
(Kinky)
Hair is a protein filament that grows from follicles found in dermis or skin
layer
Also called as Pili or Pilus
Microscopic View of Hair

3. Lengthening fibres of Keratin- Filled dead cells.
They are grouped around the semi hollow medulla, make up the cortex.
A living structure called bulb; appears as a white lump at the end of
plucked hair.
Bulb surrounds and feeds the root, Bulb lies in a pocket of epidermis called
as Follicle.

4. Hair follicle:
A hair follicle is a tiny cup-shaped pit buried deep in the fat of the
scalp. The follicle is the point from which the hair grows.
It is well supplied with minute blood vessels, and the blood passing
through them nourishes the growing region.
The temperature around the follicle is normal body temperature, and
is not affected by cold or hot weather.
Human hair growing a little faster in winter than in summer.

5. The hair follicle can be divided into two regions:
The hair bulb :
The hair bulb lies inside the hair follicle. It is a structure of actively
growing cells, which eventually produce the long fine cylinder of a
hair.
New cells are continuously produced in the lower part of the bulb.
As they grow and develop they steadily push the previously formed
cells upwards.
When the cells reach the upper part of the bulb they begin to
change, and they arrange themselves into six cylindrical layers, one
inside the other. The inner three layers of cells become the actual
hair. The outer three layers become the lining of the hair follicle -the
inner root sheath.

6. Special cells in the hair bulb produce the pigment that colors the hair.
The pigment is called melanin, and these cells are known as melanocytes.
As the developing hair moves upwards in the follicle the melanin is
carried upwards in the inner part of the hair.

7. Hair follicles are made up many different components, but these are the
four key structures.
Papilla
The papilla is made up of connective tissue and blood vessels that nourish
growing hair. It exists at the very base of a hair follicle.
Germinal Matrix
The germinal matrix, which is also referred to as the "matrix," is where
cells produce new hairs as hairs die and fall out. It is also located in the
lower region of the hair follicle.
Bulb
The bulb is a bulb-shaped, rounded structure at the bottom part of the
hair follicle "stocking" that surrounds the papilla and the germinal matrix
and is fed by blood vessels. This is the living part of the hair. In fact, hair
that is visible above the surface of the skin is actually dead.
The bulb holds several types of stem cells that divide every 23 to 72 hours,
faster than any other cells in the body. The bulb also contains hormones
that affect hair growth and structure during different stages of life, such as
during puberty and during pregnancy.

8. Bulge
The bulge area is located in the middle part (also known as the isthmus)
of the hair follicle. It contains stem cells that divide and regenerate not
only new hair follicles but the sebaceous glands and the epidermis, too.
The bulge also provides the insertion point for the arrector pili—a tiny
band of muscle tissue. The contraction of these muscles is what causes
hairs to stand on end when you get goosebumps.
The hair shaft :
This is the part of the hair that can be seen above the scalp. It consists
mainly of dead cells that have turned into keratins and binding material,
together with small amounts of water.
Terminal hairs on the head are lubricated by a natural oil (sebum) produced
by the sebaceous glands of the follicles.

9. Hair Shaft
Composed of:
Cuticle—outside covering, made of overlapping
scales, Thin-colorless-serves as a protector of the
cortex
Cortex—middle layer made of keratin and
embedded with pigment; also contains air sacs
called cortical fusi, provides strength –color –
texture
Medulla—innermost layer running down the
center of the cortex, present in large thick hairs.

11. Cuticle : A healthy cuticle is more than just a protective layer. Much of the shine that makes
healthy hair so attractive is due to the cuticle. Intact cuticle cells are smooth and glossy, and
reflect light from their surfaces. This, together with the pigment within the cortex, gives hair its
characteristic appearance. Black hair reflects less light than blond hair does. Black hair appears
glossier, however, Because the bright bands of reflected light Contrast more sharply with the
darkness of the rest of the hair.
Human hair growing a little faster in winter than in summer.
The Cortex
The cortex gives the hair its shape.
It has two major characteristics:
Melanin—pigment granules that give hair its color
Cortical fusi—air spaces, usually found near the root but may be found
throughout the hair shaft.

12. Side Bonds of the Cortex
Side bonds-link the polypeptide chains (long chain of amino acids linked
together by peptide bonds) together; responsible for the strength and
elasticity of human hair
Hydrogen Bond- weak, physical cross-link bond that is easily broken
by water or heat
Salt Bond- weak, physical cross-link bond that is broken by alkaline or acidic
solutions
Disulfide Bond- strong, chemical side bond; can be broken by extreme
heat, some high-temp styling tools, permanent waves and chemical relaxers
Hair Pigment
Melanin- the tiny grains of pigment in the cortex that give hair its natural
color
Eumelanin- provides natural dark brown to black hair color
Pheomelanin- provides natural colors ranging from red to ginger to yellow
and blonde ton

13. The Medulla
The medulla is the hair core that is not always visible. The medulla comes
in different types and patterns.
Types:
• Intermittent or interrupted
• Fragmented
• Continuous
• Stacked
• Absent—not present

14. Chemical Composition of the Hair
Keratinization-
It process by which newly formed hair cells in the hair bulb mature, fill
with keratin, move upward, lose their nucleus and die.
COHNS- major elements that make up the human hair: Carbon, Oxygen,
Hydrogen, Nitrogen, Sulfur

15. HAIR GROWTH
Two main types of hair found on the body are Vellus Hair and Terminal hair.
Vellus hair (lanugo hair)
short, fine, unpigmented, downy;
appears on parts of the body that are normally consideredchairless(forehead, eyelids,
bald scalp);
almost never has a medulla; helps with the evaporation of perspiration; women
normally retain 55% more vellus hair than men
Terminal hair
long, coarse, pigmented hair found on the scalp, legs, arms, and bodies of both males
and females; it usually has a medulla

16. Hair Growth
Anagen—hair is actively growing; lasts up to 5 years ( 1000 days or more)
Catagen—hair is not growing; a resting phase (10 days)
Telogen—follicle is getting ready to push the hair out; lasts
two to six months (101 days)
Each strand of hair on the human body is at its
own stage of development.
Once the cycle is complete, it restarts and a new strand of hair begins to
form.
The rate or speed of hair growth is about 1.25 centimetres or 0.5 inches
per month, or about 15 centimetres or 6 inches per year.

18. Hair Cycle
• The process of hair growth has three phases:
Anagen: This is the active growth stage of the hair fiber and can last from 2- 7 years. At
any given moment 80-85% of our hair is in the anagen phase.
Catagen: Sometimes referred to as the transitional phase, which is when hair growth
begins to “shut down” and stop activity. It generally lasts 10- 20 days.
Telogen: This occurs when hair growth is completely at rest and the hair fiber falls out.
At any given time, 10-15 % of our hair is in the telogen phase, which generally lasts
100 days for scalp hair. After the telogen phase, the hair growth process starts over
again to the anagen phase.

19. ANAGEN PHASE
The anagen phase is known as the growth phase.
This is the phase where the hair physically grows approximately 1 cm per
month.
It begins in the papilla and can last from two to six years.
The span at which the hair remains in this stage of growth is determined
by genetics.
The longer the hair stays in the anagen phase, the longer it will grow.
During this phase, the cells in the papilla divide to produce new hair
fibers[contradictory] and the follicle buries itself into the dermal layer of
the skin to nourish the strand.
About 85% - 90% of the hairs on one's head are in the anagen phase at
any given time

20. CATAGEN PHASE
The catagen phase, also known as the transitional phase, allows the follicle
to, in a sense, renew itself.
During this time, which lasts about two weeks, the hair follicle shrinks due to
disintegration and the papilla detaches and "rests," cutting the hair strand off
from its nourishing blood supply.
Signals sent out by the body (that only selectively affect 1 percent of all hair
of one's body at any given time) determine when the anagen phase ends
and the catagen phase begins.
The first sign of catagen is the cessation of melanin production in the hair
bulb and apoptosis of follicular melanocytes. Ultimately, the follicle is 1/6
its original length, causing the hair shaft to be pushed upward.
While hair is not growing during this phase, the length of the terminal fibers
increase when the follicle pushes them upward.

21. TELOGEN PHASE
During the telogen or resting phase (also known as shedding phase) the
follicle remains dormant for one to four months.
Ten to fifteen percent of the hairs on one's head are in this phase of
growth at any given time.
In this phase the epidermal cells lining the follicle channel continue to
grow as normal and may accumulate around the base of the hair,
temporarily anchoring it in place and preserving the hair for its natural
purpose without taxing the body's resources needed during the growth
phase.
At some point, the follicle will begin to grow again, softening the anchor
point of the shaft initially. The hair base will break free from the root and
the hair will be shed. Within two weeks the new hair shaft will begin to
emerge once the telogen phase is complete. The process results in normal
hair loss known as shedding.