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An Indepth Look At The Hair Structure : Hairdressing Articles
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An Indepth Look At The Hair Structure

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An Indepth Look At The Hair Structure

Postby chris the limey » 15 Jul 2007 10:33 pm

The hair is dependent, to a large extent, on genetic factors and the environmental surroundings for its structure and form. Heredity, age, physical condition and climate all contribute to colour, strength and growth of hair.

Each different hair texture determines the quality and density of colour. Example: Negroid hair is difficult to colour because of the dense natural pigmentation.

So, before starting any type of hair colouring, it is essential to understand the basic structure of the hair.

Hair grows from the follicle—a narrow, slanting tube below the surface of the scalp. The papilla, a small concentration of living cells at the base of the follicle, multiply to eventually become hair. This process is known as mitosis. Oxygen is fed to these cells by minute blood vessels to enable the continuation of mitosis. Whilst forming and reproducing, the cells are soft but those on the outside of the group are flattened against the follicle wall.



It is these latter cells which make up the cuticle—hard, flattened, horny scales encircling the hair and overlapping one another. The cuticle can consist of ten strata layers depending on the texture and porosity of one single hair. The cuticle scales are bound together with a putty-like substance which produces a very strong, flexible arrangement of cells—this assists in protecting the more delicate inner layer (cortex).



The free end of the flat, overlapping scales (cuticle imbrications) points upwards in the direction of the hair growth. The protruding formation of the scales facilitates easy removal of flaking skin, dirt particles, etc. The nature of these scales allows quantities of sebum (natural oil) to become deposited as tiny reservoirs and keep a coating of sebum which is essential to keep the hair in a healthy and pliable condition.

The cortex (fibrous layer) is the most important layer of the hair and makes up approximately 75 to 90% of its bulk. The physical properties of the hair which depend on the cortex are:

Strength

Elasticity

Pliability

Direction of growth

Texture and quality

The cortex cells link into a continuous and elongated structure and undergo a process of \'keratinization\' as they are pushed up along the follicle and harden.



The central core of the hair is called the medulla—an irregular, honeycombed formation of soft keratin cells. Not every hair contains this, and some can have two, but this has no effect on colouring processes.

Image

Hair is built up of keratin: protein containing sulphur, carbon, hydrogen, nitrogen and oxygen. The sulphur determines the strength of the hair because these chemical links are the most difficult to break down. Like all proteins, keratin comprises chains of amino acids (polypeptides), of which there are 22 different types.
Image
In tearing a long section from a hair sample, as seen in this micrograph, magnified 400 times, many of the thread-like fibres within the fibre cable are removed from their original location or presumably even torn apart completely.

Previously untreated hair will have these chains of polypeptides intact but if the hair has already been coloured the chains are broken. Over-processing causes the chains to break and reduce in length thereby increasing the porosity. The hair becomes extremely weak and brittle.

The Hair Cycle

Individual hairs have three stages of development (altogether taking approximately three years): anagenic, catagenic and telegenic.

1. Anagenic (growth) phase is the beginning of active growth and hair that is in this phase will remain on a normal head of healthy hair for 2 to 6 years. Approximately 85% of all hair on the scalp is in the anagenic stage at any one time.

The rate of growth and length of this period determine the maximum length of the hair. It is because of the variations in this period that some people are able to grow their hair longer than others. Contrary to popular belief, the anagenic stage is not affected by cutting, although if a client wants long hair it must be cut regularly to avoid the risk of breakage and deterioration in condition. The hair bulb is nourished by the blood circulation and provided with sensitive nerve fibres so if the hair is subjected to tension during this phase a sensation of pain or discomfort is experienced.

2. Catagenic (transition) is the second development phase. Growth ceases in the follicle and a block of cells forms a club-like mass in the papilla. Approximately 1% of the hair only is in this transitional stage. No further growth takes place until after the final stage ...

3. Telegenic (resting) phase: The follicle shrinks and the formed hair travels upwards and is held in place by the club-like mass. Approximately 14% of all hair is at any one time in the telegenic phase. After this resting period, the old hair is shed and the process repeated. The new hair either pushes up or grows past the block of cells.

Image
The picture above shows, magnified 400 times, a healthy, undamaged hair that has been tied into a tight knot
Image
Hair that has been damaged by improper care and handling loses the binding property between the layers, as shown in the below, magnified 400 times.


Natural Pigmentation

The hair\'s natural colour is an inherited characteristic. The main pigment in the hair is melanin which is formed in the melanocytes. These are cells on the dermal papilla, responsible for the introduction of molecules of pigment into the cortical cells which eventually form the cortex of the hair.



Melanin starts as a colourless substance known as tyrosine containing small quantities of amino acids. This is acted upon by an enzyme and changes into a black pigment. The granules of pigment form in different shapes and sizes. Generally, the larger the granules the darker the hair and, conversely, the smaller the granules the lighter the hair.



Grey hair is a mixture of white (colourless) hair and the existing natural colour. This is caused by the loss of activity in the melanocytes preventing formation of melanin molecules. Greying is not necessarily due to ageing but can be attributed to serious illness, sudden shock or a lack of vitamins and mineral salts.



Infants often have beautiful blonde hair which gradually changes to a darker mousy colour when they reach puberty. This is due to the metabolic change of hormone balance.



All natural hair colour is a mixture of black, brown, red and yellow pigment.


Examples

Dark Brown hair comprises approximately the following percentages of these four colour pigments:

Black 40%

Brown 30%

Red 20%

Yellow 10%



Light Brown hair has less black but more yellow pigment:
Black 20%

Brown 30%

Red 20%

Yellow 30%

Natural Ash Blonde or light mousy colours are predominantly yellow:

Black 5%

Brown 5%

Red 10%

Yellow 80%



Generally, the skin is losing some of its natural pigmentation when hair starts turning white. If a client comes into the salon asking to return to her original colour it may not be advisable. Her natural colour could have suited her once but will not necessarily do so now as her complexion has probably changed.
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chris the limey
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Re: An Indepth Look At The Hair Structure

Postby Paolo » 07 Oct 2010 07:41 am

This is an excellent article!
Paolo works with Pro Hair Biosystems Limited
The UK distributor for ProFusion shampoo and conditioner, formulated to prevent hair loss in adults.
http://www.prohairbiosystems.com
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Re: An Indepth Look At The Hair Structure

Postby chris the limey » 07 Oct 2010 02:55 pm

Crikey Paolo.

I forgot ever writing this.

It's quite scary...the older I am getting, the more I am forgetting! I just learned something from my own article. :blush:
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