Hair Structure: The Facts
What is hair?
This page explains hair structure in a simple, easy to follow way.
First of all, hair is formed within the skin, so it's important to understand the
basic structure of skin as well as hair.
So, read the bullet points below to quickly learn all about the main
features of skin and hair structure.
Please refer to the diagrams for those words shown in bold.
Also note that, since hair and skin structure are both quite complex,
only the most relevant details have been given...
- Your skin is the largest organ in your body. It
has various functions including temperature regulation, excretion,
protection against sun, rain, bugs, infection, etc.
- Skin has two main parts - the epidermis and
- The epidermis has five
layers. The uppermost layer is called the horny layer and forms the
surface of the skin. This is made from dead cells that are continuously being
shed (brushed or washed off) and replaced from below.
- The lowest layer of the epidermis is the germinating
layer (or basal layer). This region is constantly growing and
dividing into new cells, and pushing the old cells up towards the
surface of the skin.
- Below the epidermis is the dermis.
The dermis is the thickest part of the skin and contains blood vessels
to supply the nutrients needed for skin cells to grow.
Before hair growth can begin, a hair follicle
(pouch) must first be created - the germinating layer of the epidermis
grows downwards into the dermis, and forms the outside of each hair
- The dermis grows up into the base of the
follicle forming the dermal papilla. Blood vessels
can then enter the papilla and provide the nutrients to grow the hair
- The bottom of the follicle enlarges into an
area of actively growing cells called the hair bulb.
- At the base of the hair bulb, the germinating
layer becomes continuous with the outer root sheath
(this forms the inner wall of the follicle).
- The outer root sheath extends into the germinal
matrix (the hair root) which then
surrounds the dermal papilla. The germinal matrix contains stem cells
and forms the region where hair growth takes place.
- The peripheral area of the germinal matrix
grows the inner root sheath (this is the white
thickening at the end of a hair shaft if it is pulled out).
- The central area of the germinal matrix grows
the hair shaft. These cells constantly divide pushing the older ones
upwards. Initially, the cells are alike, but as they move up the
follicle they begin to change shape and keratin
(a protein) develops within the cells.
- The different types of hair cell are formed
(cuticle, cortex and medulla). By the time these cells are one third of
the way up the follicle, they are fully hardened (keratinized) and have
- A sebaceous gland lies
within each follicle. Sebaceous glands produce an oily substance called
sebum from a duct that opens into the hair follicle about halfway down
from the skin surface.
- The follicle has a bulge
which lies directly below the sebaceous gland duct in the outer root
sheath at the attachment point of the arrector pili
muscle. The bulge produces
stem cells that regenerate the follicle during the hair growth cycle.
- Hair structure of the shaft (i.e., a strand of
hair) has three layers: the cuticle (outer layer), the cortex (middle
layer) and the medulla (inner layer).
- The medulla is a honeycomb
keratin structure with air spaces within it.
- The cortex gives
flexibility and tensile strength to hair and contains melanin granules,
which give hair its color (see Hair
pigmentation section below).
- The cuticle is made from 6
to 11 layers of overlapping semi-transparent scales (which make the
hair waterproof and allow it to be stretched). Someone with thick,
course hair will have more overlapping layers of cuticles than someone
with fine hair.
Skin and hair
Skin color - inside the germinating
layer of the epidermis, cells called melanocytes produce melanosomes
(these are small packets that contain melanin granules). The
melanosomes then spread upwards through the epidermis and accumulate
just above the nucleus within skin cells - this gives protection
against UV radiation. Darker skin contains more melanin and so has more
protection against the sun.
Hair color - within the dermal papilla
at the base of a follicle, melanocytes produce melanin granules. Then,
as germinal matrix cells are produced, melanin granules pass into the
cells which then develop into the cortex (the middle layer) of a hair
shaft to give hair its color.
There are two types of
melanin: eumelanin is dominant in brown and black hair, and pheomelanin
is dominant in ginger and blonde hair. Without melanin granules, the
partly hollow hair appears gray. Hair that is completely absent in
melanin is white.
Both hair and skin are classed as epithelial tissue (i.e., tissue that
lines cavities and surfaces of the body, and also forms several
glands). The structure of
hair, nails and the outer layer of the skin are largely composed of
Keratin is a very hard structural protein that is used to protect and
support the body by forming tough, insoluble structures that are
arranged in layers.
In hair, it forms long filaments that provide hair
structure and strength, and is a key component in all three hair shaft
layers (cuticle, cortex and medulla).
In mammals, keratin forms hair, hooves, horns, skin and nails. Only
mammals have hair, but amphibians, reptiles, birds and some fish also
use keratin (i.e., for claws, feathers and scales).
page - Hair Growth Cycle.
Hair Structure and return to Hair Growth index.
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