This document discusses the biology of hair. It explains that hair is made up of keratin protein filaments and protects the body from external particles. Hair grows from follicles below the skin and is composed of three layers - the medulla, cortex, and cuticle. The hair follicle contains the germinal matrix that produces new hairs and the bulb that nourishes hair growth. Hair grows in cycles, with the anagen phase being the active growth phase that can last 3-4 years.

1. HAIR BIOLOGY
The Biology of the Hair

2. What is hair
 Hair is a simple structure that is made up
of Protein filaments called Keratin.
 Hair acts as a barrier to foreign particles.
 It's an important part of appearance and
creates gender identity.
 Hair is the only body structure that can
completely renew itself without scarring.

3. HAIR
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4.  Hair is made up of two separate structures
 The hair follicle: which exists below the
skin.
 The hair shaft: which is the hair that we
see.

5. HAIR FOLLICLE: the living part of the
hair
 contains the germinal matrix, which is where cells produce new hairs.
 Contains the bulb, which is the stocking-like structure that surrounds the
papilla and germinal matrix. It's fed by capillaries.
 The follicle is surrounded by an inner and outer sheath that protects and
molds the growing hair shaft.
 The inner sheath follows the hair shaft and ends just before the opening of
the sebaceous gland.
 The outer sheath continues all the way up to the sebaceous gland

6. HAIR FOLLICLES

7. HAIR SHAFT: the dead hair we can
actually see.
 The innermost layer: This is called the medulla. Depending on the type of
hair, the medulla isn't always present.
 The middle layer: This is called the cortex, which makes up the majority of
the hair shaft. Both the medulla and the cortex contain pigmenting cells that
are responsible for giving hair color.
 The outermost layer: This is called the cuticle, which is formed by tightly
packed scales in an overlapping structure that resemble roof shingles. Many
hair conditioning products are formulated to even out the cuticle by
smoothing out its structure.

8. The growth cycle
 The anagen phase is the active or growth phase of the
hair. Most hair is constantly growing and spends three to
four years in this stage
 The catagen phase is a transitional stage, and 3% of all
hairs are in this phase at any given time. It lasts for two
to three weeks
 The telogen phase is the resting phase, which lasts for
about three months and accounts for 10% to 15% of all hair

9. THE GROWTH HAIR CYCLE
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10. REFERENCES
 Heather Brannon, MD. The Biology of the Hair. Available
at:https://www.verywell.com/the-biology-of-hair-1068785. Updated June 24,
2017.