Hair

August 20, 2015

I begin my journey by trying to understand exactly what hair is and why it is so important… after all, hair causes movements and fashion fads; but do we understand the source of these strands we often treat as just an accessory?

Hair is defined as any of the fine threadlike strands growing from the skin of humans, mammals, and some other animals. (source Wikipedia)

Our strands are made up of about 91% protein (http://www.hairfinder.com/hairquestions/hairgrowth.htm).  Keratin is the fibrous structural protein that makes up the outer layer of our skin.  It is also the key component of our nails; it is tough and completely insoluble, which means is cannot be dissolved, in either hot or cold water.

The length of keratin fibers depends on their water content.  Complete hydration increases their length by 10-12 percent. (cite online source)

is this why water is so moisturizing and vital for hair growth and health?

Hair: It’s Structure

A strand of hair is made up of the hair shaft and the hair root, called the hair follicle.  Hair grows from hair follicles, which are embedded below the skin on your scalp.  The root is the strand of hair that is in the hair follicle; the hair strand is the part of the hair we can see and touch and style.  The bulb is at the base of the root in the hair follicle and holds the nutrients are converted into new hair cells.

hair follicle

Hair: Its Growth

It all begins in the hair follicle – this is the only place where there is life in the hair.  The part of the hair that we can see is the hair shaft, and has no biochemical activity – we call this dead.  The bulb is the base of the hair’s root and it holds the cells which produce the hair shaft.  Then we have the sebaceous glands, which produce oil and lubricate the hair; and muscles called the arrector pili, which make the hairs stand up.  You know, like goose bumps.

Hair grows everywhere on the body except for the palms of the hands, soles of the feet, and on the lips.

Hair growth takes place in four-phase cycles:

  1. Anagen is the active growth phase, the length of which varies greatly between people and individual hair follicles. Anagen lasts for two to seven years on the human scalp, but for only months on the eyebrows.
  2. The growth phase is followed by Catagen, a brief transition phase lasting for approximately two to four weeks.
  3. After Catagen, the Telogen phase, a resting phase, begins. Hairs in the telogen phase are dead and are called club hairs. Many club hairs are shed from the body daily. The telogen phase lasts about three weeks for hairs on the human scalp.
  4. The final stage of the hair follicle cycle is exogen, a shedding phase in which one of many hairs that may arise from a single follicle is shed.

The hair strand, or shaft, is the part of the hair strand you can see – growing above the scalp.  It consists of three layers: the cuticle, the medulla, and the cortex.

hair strand

the Cuticle

The hair cuticle is the outside of the hair shaft – think of a roof shingle – it is hard and has a layer of overlapping cells.  It’s is formed from dead cells that form scales and that gives the hair shaft strength by providing protection.  The hair cuticle is the first line of defense against all forms of damage; it acts as a protective barrier for the softer inner structure including the medulla and cortex.  The cuticle is responsible for much of the mechanical strength of the hair fiber.  A healthy cuticle makes healthy shiny hair, and since it controls the water content of the fiber, the hair cuticle is said to be water resistant.  Cuticle cells may be long, tapered to a point, egg-shaped, or flattened.

The Cuticles are often damaged by excessive mechanical manipulation such as brushing, heat (like curling irons) or chemical processing (like perms or texturizers). Everyday elements, such as the sun or wind can cause wear and tear on hair, as well, and damage the hair cuticles.  Even though the cuticle is the outermost layer of the hair, it does not give the hair its color because it has no melanin, which is the pigment that responsible for color.  The color of a person’s hair actually depends on what type of melanin they have, which is found in the cortex.

the Cortex

The cortex of the hair shaft is located between the hair cuticle and medulla and is the thickest hair layer.  It also contains most of the hair’s pigment, giving the hair its color – this is melanin, which is also found in the skin.  The distribution of this pigment varies from animal to animal and person to person.  In humans, the melanin is primarily denser nearer the cuticle whereas in animals, melanin is primarily denser nearer the medulla.

the Medula

The medulla is the innermost layer of the hair shaft, is not always present and is an open, unstructured region that is nearly invisible.  Scientists are still uncertain about the exact role of the medulla, but they know it serves as the pith or marrow of the hair; and they speculate that it is primarily an air space that is more prominent in grey or white (‘in-pigmented’) hair.

about that Color

All natural hair colors are the result of two types of hair pigments – both produced inside the hair follicle and found in the fibers.  (1) Eumelanin is the dominant pigment in brown hair, and black hair; (2) pheomelanin is dominant in red hair.  Blond hair is the result of having little pigmentation in the hair strand.  Gray hair occurs when melanin production decreases or stops.

Keratinization

“As hair is pushed up through the hair follicle and towards the surface of your scalp, it goes through a process known as keratinization.  The hair cells fill with fibrous proteins and lose their nucleus. By the time the hair reaches the surface, it’s nothing more than a complex system of interwoven protein-rich fibers.” (http://growhairguru.com/what-is-hair-made-of/)

Proteins and Hair
Protein makes up 91% of your hair.  “Proteins are series of long, connected amino acids known as polypeptides.  Polypeptides can form side bonds with one another, leading to the thick strands of hair you recognize.  There are three types of bonds that hold hair together.  The weakest bonds can be altered with the use of heat and water, giving you the ability to style your hair with products like curling irons and flat irons.  Other bonds can be altered with permanent chemical treatments such as waves and relaxers.” (http://growhairguru.com/what-is-hair-made-of/)

Want more Hair-Science(ish)?  Stay tuned for Hair Texture & Density, coming up next…

sources:
(so, okay.  I did pretty darn well in school, but I borrowed knowledge for the purpose of this post – knowledge is power and all!)
wikipedia: “Hair”
WebMD: “Hair, Human Anatomy”

 

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