so what do you have to remember from this chapter?

Some usefull conclusion notes from the hair structure chapter:

• The dermal papilla is well supplied with minute blood vessels,
  and the blood passing through them nourishes this growing region.

So if you want you hair to grow you have to "feed" good this growing regions through blood vessels: eat food necessary for your hair and do some activities to increased blood flow to the hair folicles (like scalp massage, brushing your hair while you are bent over at the waste, standing on your head, will help to increase blood flow to the head.Watch out for dizziness!)

• When hair is wet the cortex swells and the edges of the cuticle scales tend to lift.

So don't comb or brush your wet hair, because you can easealy damage it. Be careful with your wet hair!

• Chemical treatments of hair such as perming and bleaching can alter the cortex after repeated damage, and change the hair's elasticity. The cuticle can also be damaged in the same way by too much blow drying, curling irons that are too hot, and the effects of wind and sun. The hair becomes increasingly porous, and water can then pass in and out of the cortex. Over-porous hair is dry, and tends to develop split ends.At least 17% of humidity is required by the hair fibers to maintain a healthy appearance.

So you have to avoid perming, bleaching, curling irons. If you use a blow fryer, don't use it on your ends! This is the most delicate bit of your hair as they are usually about 6 years old! They needed to be treated really well if you don't want to be cutting off damaged and split ends every month.

• The dermal papilla cells are The growing region of the hair is dermal papilla, which lies at the base of the hair bulb

So it"s a myth telling that hair will grow faster, when you cut the end. You will simply stop your split end dividing.

• The telogen phase is the time at which a new hair begins to grow from the hair follicle. As it grows upwards the old hair will be shed naturally or may be pulled out, which happens easily and painlessly with telogen hairs.

So don't worry, if you loose 70-80 hairs per day. It's natural phase of the hair cycle, which means that instead of sheded hair the new one grow from the same follicle.

• Many alcoholics have poor hair growth or even hair loss because their way of life tends to lead to malnutrition. So too does starvation: people who go on a crash diet may start to lose their hair some six to ten weeks later. Treatment of cancer with drugs also influence the hair growth. It may even cause apparent complete hair loss. Experiments have established that there is also the link between the immune system and hair growth cycle. Significant hair loss can also be caused by severe psycho emotional stress.

So eat plenty of healthy food, stay away from drugs and alcohol and have nice dreams!

What does influence hair growth?

No one can answer this question with certainty.
What we do know is that it takes a lot to stop hair growing!

General health and nutritional factors are increasingly believed to be important for healthy hair growth. We do know that serious anaemia affects hair growth. So too does starvation: people who go on a crash diet may start to lose their hair some six to ten weeks later. Many alcoholics have poor hair growth or even hair loss because their way of life tends to lead to malnutrition.
Some minerals may be particularly important for hair growth. For example, some people who lack zinc in their diet produce only fine, sparse hairs and even lose their hair. Vitamin B, also known as panthenol, plays a part in hair growth. It also improves the physical properties (elasticity, strength and gloss) of the hair shaft.

The hair cycle for each individual hair is influenced by the levels of various hormones in the blood. Thyroid hormone speeds up growth in resting hair follicles. Steroids taken by mouth slow it down, though steroids inhaled for the treatment of asthma do not affect hair growth. The hair of the scalp is, however, most sensitive to the effects of male hormones (androgens), which are in the blood of people of both sexes (only in different proportions in men and women). Androgens are the most important factor regulating hair growth, and also the thickness of the hair shaft. Female hormones (oestrogens), which both sexes have too, slow down hair growth during the growing period but also make that period longer. Many women notice a difference in their hair growth during pregnancy. At this time women have vast amounts of oestrogen in their blood, far outweighing their male hormones. It is the balance between the male and female hormones which decides the growth of the hair. At puberty the immature vellus-like hairs on our bodies can change to terminal hairs. This change results from the dramatic rise in androgen levels at that time. It is especially noticeable in young men. Young women who suffer from the condition of anorexia nervosa, however, stop having periods and produce very little oestrogen: their natural androgens tend to thicken their fine vellus-like hairs in the same way.

Treatment of cancer with drugs also influence the hair growth. It may even cause apparent complete hair loss.This is because these drugs are designed to kill cancer cells, which are cells that are growing out of control. Other cells that are growing very actively may be affected too: these may include cells in the bowel lining and also in hair follicles. This leads to a 'break' in growth and an inherent weakness. Once the drugs are stopped the patient's hair starts to grow back, but when it reaches the surface it tends to break. This is what causes the apparent hair loss. The hair that subsequently grows may look quite different from the old. This is because the growth patterns of the sensitive cells of the hair bulb may still be upset by the effects of the drug.
Experiments have established that there is also the link between the immune system and hair growth cycle. Significant hair loss can also be caused by severe psycho emotional stress.

Stages of the hair cycle

Stages of the hair cycle

Between starting to grow and falling out years later, each hair passes through three distinct stages. They have been given special names: anagen (the growing phase), catagen (the intermediate phase) and telogen (the shedding phase). We shall look at these three stages in turn.

Anagen (the growing phase)

The anagen phase of a new hair starts at the moment it begins to grow. You know that at the bottom of the hair bulb there is dermall papilla. The dermal papilla is cluster of specialized mesenchymal cells ( active and dividing cells above and around the dermal papilla). They begin to grow upward to form the hair shaft.That dermal papilla cells know beforehand what size and shape of hair follicle they should form and they also retain a memory of their hair cycle clock.
What is involved in the biochemical clock mechanism inside dermal papilla cells has been considered for a long time and a number of hypotheses have been suggested, but it is still unknown as to what determines the duration of anagen within dermal papilla cells.

Near 85% of the scalp hair is under the influence of anagen phase and approximately 15% are under the telogen phase. The anagen phase of scalp hair follicles typically lasts for 2-6 years. There are exceptions though; a few individuals experience anagen growth phases for much longer durations. The maximum hair length that scalp hair can grow to is mostly determined by the duration of the anagen phase. Approximately human hairs grow at a rate of roughly 1 (10-13 mm)centimetre a month. Throughout anagen also pigment (melanin) is made.

Catagen (the intermediate phase)
The anagen phase is followed by a short resting phase. This catagen phase lasts for between two and four weeks in the human scalp. No pigment is made during that time, and the dermal papilla stops producing hair. The base of the follicle moves upwards towards the surface of the skin.

Telogen (the shedding phase)
The telogen phase lasts for three or four months. This is the time at which a new hair begins to grow from the hair follicle. As it grows upwards the old hair will be shed naturally or may be pulled out, which happens easily and painlessly with telogen hairs. The new hair emerges from the same opening at the surface of the skin as the old one, and the hair cycle begins again.

Many people worry because they often find loose hairs on their clothes, or after shampooing, and they become terrified in case they may lose some or most of their hair. If you pull the hair lightly with your hand, you may well find that a few hairs do come out. These are almost certainly hairs that are ready to fall anyway - telogen hairs. You can confirm this by looking at the roots in a good light. A telogen follicle root is a little hard, white bead. Brushed-out hairs all have this kind of root.


A normal telogen hair with a hard 'club' end, seen under (left) a light microscope and (right) an electron microscope

On the other hand, the root of a hair that is pulled out is fat, soft to the touch and sticky - it will stick to your hand, because it still carries fluid from the follicle. And pulling it out hurts! This is an anagen hair, one which was not ready to be shed.


An anagen hair that has been plucked out: notice the soft, sticky tail

The physical properties of hair

Elasticity

This is one of the most important properties of hair. Because of its elasticity, hair can resist forces that could change its shape, its volume or its length. Its elasticity lets it spring back to its original form without damage.When healthy hair is wetted and stretched, it can increase in length by up to 30% and still return to its original length when it is dried. Stretching it more than this will tend to damage it, however, leading to permanent lengthening and even breaking.The elasticity of hair depends on the long keratin fibres in the cortex. Chemical treatments of hair such as perming and bleaching can alter the cortex after repeated damage, and change the hair's elasticity. Hair with poor elasticity will stretch only to a limited extent. It will not curl, it will break easily when it is groomed and it cannot be permed satisfactorily.Both natural sunlight and artificial ultraviolet light break down chemicals in the hair and damage its elasticity in the same way that bleaching does, though to a much lesser degree.

Static electricity

When dry hair is rubbed, as it is whenever it is brushed or combed, static electric charge builds up on the hairs. This is especially noticeable in hot, dry weather. Hair has negative charges, which tend to push each other apart, and as a result charged hairs can never lie smoothly against each other. The result is 'fly away' hair, which stands out from the head and looks unmanageable.
Moisture content

At least 17% of humidity is required by the hair fibers to maintain a healthy appearance. Up to 35% of water retention is possible. Hair length may vary up to 2% depending on the air humidity. ( In 1783, Swiss physicist and geologist, Horace Bénédict de Saussure built the first hygrometer using a human hair to measure humidity. You even can make such one by yourselves! http://www.kidsgardening.com/growingideas/projects/aug03/pg1.html)

The moisture content of hair is greater when the atmosphere is moist and humid, and less when the air is dry. When hair is wet the cortex swells and the edges of the cuticle scales tend to lift.

The hair surface temporarily loses its smoothness. There is therefore more friction when wet hair is rubbed than when it is dry. This is what can lead to matting and tangles developing during over-vigorous shampooing (there is not greater static charge on wet hair than on dry).

Slight lift of the hair cuticle

Porosity

In a normal, undamaged hair shaft, very little water can get either into or out of the cortex. This is because the cuticle covering the cortex is intact, and is then almost (but not quite) waterproof.
When hair is permed or tinted, however, the chemicals have to penetrate the cortex in order to react with the keratin inside it. Increasing the temperature, or applying an alkaline lotion, separates the scales of the cuticle enough to allow the chemicals to pass through. After the processing is finished the scales gradually close up again.But if hair is processed too many times the cuticle scales may never return to their original tightness and the protection they once offered is lost. The cuticle can also be damaged in the same way by too much blow drying, curling irons that are too hot, and the effects of wind and sun. The hair becomes increasingly porous, and water can then pass in and out of the cortex.Over-porous hair is dry, and tends to develop split ends. The damaged cuticle is fragile, and the damage worsens as time goes by. The greater the damage, the more the cortex swells with water whenever the hair is washed, but the more water it loses when it dries. The repeated wetting and drying of the cortex gradually weakens the hair.Hair damaged by perming

Light reflector

A healthy cuticle is more than just a protective layer. Much of the shine that makes healthy hair so attractive is due to the cuticle. Intact cuticle cells are smooth and glossy, and reflect light from their surfaces. This, together with the pigment within the cortex, gives hair its characteristic appearance.Black hair reflects less light than blond hair does. Black hair appears glossier, however, Because the bright bands of reflected light сontrast more sharply with the darkness of the rest of the hair, as in the photograph below.

The hair shaft seen with the light microscope: light is reflected from the colorless cuticle and bent as it passes through the hair - this effect gives hair the color we see

Hair structure

A hair is a specialised outgrowth of part of the skin called the epidermis. It has two distinct parts, the hair follicle and the hair shaft.
A hair follicle is a tiny cup-shaped pit buried deep in the fat of the scalp.
Inside the hair follicle lies the hair bulb. At the base of the hair bulb is the dermal papilla.It is a structure of actively growing cells. As they grow and develop they steadily push the previously formed cells upwards. When the cells reach the upper part of the bulb they begin to change, and they arrange themselves into six cylindrical layers, one inside the other. The inner three layers of cells become the actual hair. The outer three layers become the lining of the hair follicle - the inner root sheath.

The dermal papilla is well supplied with minute blood vessels, and the blood passing through them nourishes this growing region.
Special cells in the hair bulb produce the pigment that colors the hair. The pigment is called melanin, and these cells are known as melanocytes.

As the developing hair moves upwards in the follicle the melanin is carried upwards in the inner part of the hair.In the mid-follicle region the actively growing cells die and harden into what we call a hair. As the cells below continue to divide and push upwards, the hair grows upwards too, out of the skin. It now consists of a mixture of different forms of the special hair protein, keratin.

Hair bulb

The hair shaft is the part of the hair that can be seen above the scalp. It consists mainly of dead cells that have turned into keratins and binding material, together with small amounts of water. Terminal hairs on the head are lubricated by a natural oil (sebum) produced by the sebaceous glands of the follicles.
Your smooth, glossy hairs have a more complicated structure than you might think. Each one can be compared to a tree: all its moisture lies in its centre, behind a tough outer layer of protective bark.

The outer layer of the 'bark' is called the cuticle.

It is made up of between six and ten overlapping layers of long cells. Each of these cells or scales is about 0.3 micrometres thick and around 100 micrometres long, and about 10 micrometres across. (1 micrometre, written 1 µm, is one-millionth part of a metre = one-thousandth part of a millimetre.) The scales lie along the surface of the hair like tiles on a roof, with their free edges directed towards the tip. They cover the hair surface all the way along its length

The cuticle scales lie along the surfaceof the hair like tiles on a roof

The centre part of the hair, called the cortex, makes up most of the hair shaft. It is the cortex that gives hair its special qualities such as elasticity and curl. The cortex is packed with strands of keratin, lying along the length of the hair.
Hair is surprisingly strong: a single hair can support a load of about 100 grams without breaking. You could even spin rope out of hair! Healthy hair fiber has a tensile strength around 180-190 MPa. This means hair is almost as strong as copper wire of the same diameter.The keratin protein of the cortex is responsible for this unusual strength. The long keratin molecules in the cortex are compressed to form a regular structure, which is not only strong but also flexible. Proteins are made up of long chains of amino acids. Each chain takes up a helical or coiled form, rather like a long spring, or the cable of a telephone handset.Most protein chains are made up of various mixtures of the same 20 or so amino acids. Keratin is unique in that its chains contain high concentrations of a particular amino acid called cystine. The proteins in the matrix of the hair contain the highest levels of cystine.Every cystine unit contains two cysteine amino acids in different chains which have come to lie near to each other and are linked together by two sulphur atoms, forming a very strong chemical bond known as a disulphide linkage.

Many disulphide bonds form down the length of the keratin chains, joining them together like the rungs of a ladder.The disulphide bond is one of the strongest bonds known anywhere in nature. They can only be changed by chemical methods such as perming or relaxing.But within each hair the keratin chains are also linked by bonds of a different kind, called hydrogen bonds. There are far more hydrogen bonds than disulphide linkages. The hydrogen bonds are much weaker than the disulphide linkages and more easily broken, and they give hair its flexibility. Hydrogen bonds are broken apart whenever the hair is wetted, and form again as it dries. When they break the shape of the hair changes. If the wet hair is then wound on to rollers it will form a new shape, and if it is dried on the rollers it will keep this shape.This is the basis of the setting process. The change in shape is only temporary. It is lost when the hair is dampened, because the new hydrogen bonds are broken again.

Hair also contains fats, pigment (melanin), small amounts of vitamins, and traces of zinc and other metals. Hair also contains water which, although it makes up only 10-13% of the hair, is extremely important for its physical and chemical properties. typical hair is composed of 50% carbon, 20% oxygen, 17% nitrogen, 6% hydrogen, and 5.0% sulphur. Trace amounts of magnesium, arsenic, iron, chromium and other metals and minerals are also present in the hairs.