2. Hair is one of the characteristic features of mammals and has various functions such as protection
against external factors; producing sebum, apocrine sweat and pheromones; impact on social and
sexual interactions; thermoregulation and being a resource for stem cells.
Hair is a derivative of the epidermis and consists of two distinct parts: the follicle and the hair shaft.
The follicle is the essential unit for the generation of hair.
The hair shaft consists of a cortex and cuticle cells, and a medulla for some types of hairs.
Hair follicle has a continuous growth and rest sequence named hair cycle.
The duration of growth and rest cycles is coordinated by many endocrine, vascular and neural stimuli
and depends not only on localization of the hair but also on various factors, like age and nutritional
Distinctive anatomy and physiology of hair follicle are presented in this chapter.
Extensive knowledge on anatomical and physiological aspects of hair can contribute to understand and
heal different hair disorders.
3. Nearly whole body surface is coated with the hairs except a few areas like palms, soles and mucosal
regions of lips and external genitalia.
Most of these are tiny, colorless vellus hairs.
The ones located in several areas like scalp, eyebrows and eyelashes are thicker, longer and
pigmented and are called terminal hairs.
Humans have approximately 5 million hair follicles and 100,000 of them are located on the scalp
5. Cosmetologists should study the properties of the hair and scalp so that they can differentiate between normal
and abnormal hair loss, offer a varity of chemical services to clients , and aid a client in caring for their scalp and
hair well-clients, and aid a client in caring for their scalp and hair well-being.
Trichology- study of hair and its diseases and care.
Human hair is divided into two parts:
(epi- means above or outer ; and derm- means skin so epidermis is the OUTER layer of skin)
6. STRUCTURE OF THE HAIR ROOT
Arrector pili muscle
8. The Hair Bulb
The hair bulb is a structure of actively growing cells, which eventually produce hair.
Cells continually divide in the lower part of the bulb and push upwards, gradually hardening.
When they reach the upper part of the bulb they arrange themselves into six cylindrical layers
The three inner layers become the hair, made up of the cuticlethe cortex and the medulla – although the
medulla isn’t always present in hairs with a thinner diameter.
The outer three layers become the lining of the follicle and form the inner root sheath and basement
membrane, around which lie undifferentiated cells.
Specific cells in the hair bulb, melanocytes, make the pigment called melanin that gives your hair its
9. Hair Shaft
Your hair shaft is the part of your hair that can be seen above your scalp.
It’s made of a protein called keratin, compacted and cemented together.
Keratin is a remarkably strong protein, which is very resistant to wear and tear.
It’s the same material that feathers, claws, nails and hoofs are composed of! Keratin is a sulphur-rich
protein, with strong ‘disulphide’ bonds holding the protein strands together.
This plays an important role in any chemical processing like perming and relaxing, which break
disulphide bonds and reset them to a different configuration to change the shape of your hair.
Your hair shaft is also made of hydrogen bonds, which help to give your hair its flexibility.
They are weaker and more numerous than disulphide bonds and are easily broken with the application
of water – this is what allows you to temporarily change the natural configuration of your hair with
heated styling aids after washing.
Hair shaft consists of three layers:
10. The Cuticle
• A protective layer composed of overlapping cells, like fish scales or roof tiles, but facing downwards.
• The outer cuticle holds your hair in your hair follicle by means of a Velcro-like bond.
• It also minimizes the movement of water (moisture) in and out of the underlying cortex. However,
chemical processes and weathering can lift the cuticle and disrupt this balance. When healthy, i.e.
smooth and intact, your outer cuticle gives your hair shine and protects the inner layers from damage.
• Forms your hairs’ main bulk and pigment (colour).
• It consists of long keratin filaments, which are held together by disulphide and hydrogen bonds.
• The health of your cortex depends largely on the integrity of the cuticle protecting it.
• A thin core of transparent cells and air spaces.
11. Chemical Composition of the Hair
Keratinization- 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, Sulphur
12. HAIR PIGMENT
Melanin- The tiny grains of pigment in the cortex that give hair its natural colour.
Eumelanin- Provides natural dark brown to black hair colour.
Pheomelanin- Provides natural colours ranging from red to ginger to yellow and blonde tones.
14. Anagen: Growing phase
The stages of hair growth begin with the anagen phase.
It’s the longest phase, lasting about 3 to 5 years for the hairs on your head, though for some people a
single hair could continue growing for 7 or more years.
Fortunately, the anagen phase differs with different types of hair.
For example, the anagen phase for eyebrow hairs and pubic hairs is much shorter than the phase for
your scalp hairs.
During the anagen phase, your hair follicles are pushing out hairs that will continue to grow until they’re
cut or until they reach the end of their lifespan and fall out.
At any time, about 90 percent Trusted Source of the hairs on your head are in the anagen phase.
15. Catagen: Transition phase
The catagen phase starts when the anagen phase ends, and tends to last about 10 days or so.
During this chapter, hair follicles shrink and hair growth slows.
The hair also separates from the bottom of the hair follicle, yet remains in place during its final days of
Only about 5 percent of the hairs on your head are in the catagen phase at any given time.
16. Telogen: Resting phase
The telogen phase typically lasts around 3 months.
An estimated 10 to 15 percent of your scalp hairs are in this phase.
Hairs don’t grow during the telogen phase, but they don’t usually fall out either.
The telogen phase is also when new hairs start to form in follicles that have just released hairs during
the catagen phase.
Some health experts consider the telogen phase the shedding phase, as well, but many scientists have
divided this stage into two parts: the telogen and exogen stages.
4. Exogen: Shedding phase
17. Exogen: Shedding phase
The exogen phase is essentially an extension or a part of the telogen stage of hair growth.
During the exogen phase, hair is shed from the scalp, often helped along by washing and brushing.
Losing 50 to 100 hairs per day during the exogen phase is normal.
During the exogen phase, which can last about 2 to 5 months, new hairs are growing in the follicles
as old hairs fall away.
18. How to maintain hair health during all four stages
Having healthy, fuller hair depends on genetics and hormone levels, which are largely beyond your
control, as well as manageable factors related to a healthy lifestyle and proper hair care.
Some of the best strategies for all four stages include:
Because hair is largely made of protein, you should keep up your protein intake by focusing on healthy
proteins. That includes:
•low-fat dairy products
A 2019 study in the journal Dermatology and Therapy Trusted Source also found that sufficient intake of
the following nutrients was associated with healthy hair growth:
•Iron (especially in women)
Zinc, folic acid, and vitamin B12 may also be associated with promoting healthy hair growth.