Anatomy of Hair

Anatomy of Hair

At the base of the hair follicles are sensory nerve fibers that wrap around each hair bulb. Bending the hair stimulates the nerve endings allowing a person to feel that the hair has been moved. One of the main functions of hair is to act as a sensitive touch receptor. Sebaceous glands are also associated with each hair follicle that produce an oily secretion to help condition the hair and surrounding skin.

It is commonly believed that a man is more likely to have hair loss if his mother’s father also had hair loss.

It appears that hair loss is inherited but the details as to how remain unclear. The following are possible ways it could be inherited:
• A problem with a single gene that may or may not affect all men the same

• A problem with a pair of genes that are related to sex chromosomes

• A problem with multiple genes

• A person who experiences hair loss can have a family history of hair loss on either side of the family.  On the other hand, there may be no family history of hair loss. The good news is – if you have someone in your family who has experienced hair loss, it does not mean that you too will experience hair loss.
Hair is much more complicated than it appears. Not only is hair important to both men and women but hair helps transmit sensory information and creates gender identity. Hair is remarkable in that it is visible on all major surfaces of the body and is the only structure that is completely renewable without scarring. The information that follows explains just what hair is and exactly how it functions.

Hair Origin

A developing fetus has all of its hair follicles formed by week 22. At this time there are approximately 5 million follicles on the body. About one million of those are on the head and approx. 100,000 are on the scalp. This is the largest number of follicles we will ever have as hair follicles do not form during life. As the size of our bodies increases with age, the density of the hair follicles on the skin decreases.

Hair Anatomy

Hair has two separate structures – the follicle in the skin and the shaft that we see.


The follicle is a stocking-like structure that contains several layers. Each of those layers area responsible for different jobs. At the base of the follicle is a projection formed similar to sticking a finger in the bottom of a stocking and slightly pushing outward. This projection is called a papilla and it contains capillaries, or tiny blood vessels, that feed the cells. The living part of the hair is the bottom part of the stocking surrounding the papilla called the bulb. This bottom part is the only part fed by the capillaries. The cells in the bulb divide every 23 to 72 hours which is said to be faster than any other cells in the body.
The follicle is surrounded by two sheaths —  an inner and outer sheath. These sheaths protect and mold the growing hair shaft. The inner sheath follows the hair shaft and ends below the opening of a sebaceous (oil) gland, and sometimes an apocrine (scent) gland. The outer sheath continues all the way up to the gland. A muscle called an erector pili muscle attaches below the gland to a fibrous layer around the outer sheath. When this muscle contracts, it causes the hair to stand up.

The sebaceous gland is important because it produces sebum which we refer to as a natural hair conditioner. Increased sebum is produced after puberty but usually decreases as we age. This is especially true for women. Sebum production is also said to decrease with age in men, but far less than in women.
The hair shaft is made up of dead, hard protein called keratin and consists of three layers.  The inner layer is called the medulla and may not be present.

The next layer is the cortex which makes up the majority of the hair shaft and the outer layer is the cuticle. The cuticle is formed by tightly packed scales in an overlapping structure similar to roofing shingles. Many hair conditioning products attempt to affect the cuticle. Pigment cells can be found distributed throughout the cortex and medulla giving the hair it’s characteristic color.

Hair and the Aging Process
For many of us, as we age, our hair thins resulting in eventual hair loss and a reduction in the active growing cycle or anagen phase of hair growth. The subcutaneous fat layer of the scalp also thins and hair becomes more brittle.

The ability of the hair cortex to absorb melanin begins to diminish and the hair begins to lose its youthful color and shine. What many of us do not realize is that our hair grows from a vital point of the skin called the follicle. Unlike the visible portion of the hair that is comprised of keratin and is “non living,” the portion of the hair that resides below the scalp within the follicle is full of activity and life. The hair fiber originates at a terminal point called the hair bulb where living dermal papilla cells grow, divide and absorb melanin. By addressing hair and scalp health at the cellular level, this formula provides healthier, thicker, younger hair.

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