HAIR SCIENCE - PART 1 by Tracy Hayes

Overview Tracy Hayes’ Hair Science Lecture series begins with an in-depth look at the structure and growth cycle of hair. In this video, Tracy focuses on the the biological structure of hair and its properties. She also provides in-depth information about the 3 stages of hair growth, environmental and health factors affecting hair growth and hair damage.

Skill Level Beginner

Technical Skills Anagen - Catagen - Cortex - Cuticle - Dermal - Density - Dermis Elasticity - Environmentally Damaged Hair - Hair Follicle - Hair Root - Keratin Medulla - Melanin - Papilla - Porosity - Sensitised Hair - Telogen - Terminal Hair Texture - Vellus Hair

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Like the rest of the human body, hair is very much alive and sensitive to our moods or the changes in the weather. The part of the hair that we see is in fact dead. It is under the epidermis, in the root, that the vibrant life is going on.

We often hear clients say that their roots have grown, or they have grey roots. However, this is untrue, as the real roots cannot be seen. Hair roots are protected in the depths of the dermis in a small pit known as the hair follicle, where they are actively growing and are therefore the living part of the hair.

As the hair grows, it becomes hardened and emerges from the surface of the skin as dead keratin. Although you can damage the hair shaft, to actually kill the hair you must damage the follicle.

The part of the hair that is seen above the surface of the skin is the hair shaft, and unless the hair has been cut, the tip is always pointed. The hair shaft is composed of a dead, tough horny protein material called keratin.

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The diameter of a single hair is 58 - 100 microns. (1 micron = 1/1000th of a millimetre) The average amount of hairs of any individual ranges from between 80,000 to 150,000 hairs. Blonde hair is normally finer, but has more hairs on the head, followed by brunettes, and then red heads.

The average weight of a head of hair is 5 to 200 grams, depending on the length and thickness of the hair. When the hair is shampooed, it then weighs an extra 30% of its overall weight as long as the hair is healthy and 45% when the hair is porous or damaged.

An average hair grows 1 cm per month, which works out to a daily growth of 0.03 cm per day and a yearly growth of 12 cm per hair.

We naturally lose between 50 -100 hairs per day. A normal and healthy strand of hair can stretch 50% of its own length before it will break. Hair grows faster in women than in men and grows faster in summer than in winter months. This is due to diet, sunshine and a better frame of mind.

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Shorter hair appears to grow faster than longer hair. Hair goes white, it does not go grey. This is due to the melanin in the hair dying, although the reason for this is currently unkown. Men go bald, and women wrinkle, this is due to the different hormones produced by men and women.

What is hair made of?

The protein Keratin is the main ingredient of the hair make up. Hair also contains water, lipids, traces of mineral elements and melanin. Within the cortex it is almost like a rope or a cable.

Hair can be very strong and can withstand the strain of 11 grams, which means that an average head of 120,000 hairs could cope with 12 tons of pressure if the scalp was strong enough. Keratin within the cortex provides this strength and is made up of 18 amino acids including cysteine. Cysteine is rich in sulphur and plays an important part in hair growth by increasing the diameter of the hair shaft.

Types of Hair

Hair can be divided into 2 types - Terminal and Vellus.

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Terminal

This is the strong hair that we cut, which includes the hair on the scalp, the beard, underarm hair and pubic hair.

Vellus

This is the fine downy hair, which covers the rest of the body, apart from the soles of the feet and palms of the hands. Vellus hair provides the human body with warmth and protection.

There are several contributing factors involved in the re-growth of hair, including: Health and diet Age and sex Hormone balance and hereditary factors Climate Physical condition Chemical Effects of disease

Properties of Hair Elasticity

This is due to the structure of the cortex. It is like a bundle of small coiled springs. A normal and healthy strand of hair can stretch 50% of its own length before it will break. After it is pulled it returns to its original length, which gives the hair its natural bounce.

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Porosity

Liquids can pass between the cuticle scales into the cortex. There are different levels of porosity depending on the state of the cuticle and the condition of the hair.

Texture

This may vary from thick or course hair to very fine hair, depending on different factors such as: Hair thickness Roughness of the cuticle Moisture level of the cortex Length of hair, as short hair tends to feel stiff, and long hair seems soft.

Hair Damage

What causes hair damage?

Age and Friction

The ends of the hair shaft are older and have had more exposure than any re-growth, so will be more prone to damage. The hair around the face can suffer damage due to friction as hair may be brushed and combed excessively or badly or constantly pushed away from the face. Excess massage while shampooing and towel drying or brushing wet hair while blow drying and combing out tangles can also damage the hair.

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Heat and Chemicals

Using straightening irons, heated rollers, tongs or hot dryers incorrectly can cause heat damage to the hair. Heat can dry out the hair’s natural moisture and cause breakage or spilt ends. The cuticle may be damaged by strong alkaline treatments. Over-processing can damage the links inside the cortex. There may be breakage of the hair shaft due to excessive oxidation in bleaching.

Natural Elements

The ultra violet light in sunshine can reduce the strength of hair. Heat can dry the hair and cause breakage or split ends.

The life of a single hair varies between individuals. Many animals moult when lots of their follicles enter the resting stage at any one time. Humans have a constant daily loss of between 20 - 100 hairs. If this number increases over 100, the hair loss is too great and baldness will eventually happen.

Hair Growth

There are 3 stages to hair growth: Anagen - active growth which lasts 1 1/2 years to 7 years. Catagen - change/breakdown which lasts 2 weeks. Telogen - resting which 3 to 4 months.

Anagen

Hair grows at a rate of about 1 cm a month. If the anagen stage lasts only 2 years, that person cannot grow their hair longer than approximately 30 cm. If anagen lasts up to 7 years, the hair will grow longer than this. New anagen hairs grow faster than old ones. About 85% of scalp hair are in the anagen stage at any one time.

Catagen

The period of growth is followed by a period of change before the follicle enters the restoring stage. Catagen will last for approximately 2 weeks, when the activity stops and no new cells are produced. Furthermore, the production of melanin will stop. The lower part of the hair separates from the base of the follicle forming a club hair. The hair will rise as the follicle shortens. The root germ remains attached to the cells previously in the dermal papilla. About 1% of scalp hairs are in the catagen stage at any one time.

Telogen

The resting stage of the follicle lasts 3 to 4 months. The follicle remains shortened and dormant, with the root germ still in contact with the dermal papilla. There are 14%-15% of scalp hair in the telogen stage at any one time. At the end of the resting stage, the new follicle begins from the root germ, and returns back to anagen.

Hair Structure

Hair is composed of a strong structural protein called keratin. This is the same protein that makes up the nails and outer layer of skin.

Each strand of hair consists of 3 layers.

Medulla

The inner most layer, which is only present in large thick hairs.

Cortex

The cortex is the most important part of the hair. It provides the strength, the colour and the texture of the hair. The cortex consists of fibres bunched together within which are small coiled springs that give the hair its elasticity. The cortex also contains granules of the pigment melanin, which gives the hair its colour.

Cuticle

This is the outermost layer. The cuticle is thin and colourless and serves as a protector of the cortex. If you run your fingers towards the root of the hair, it will feel rough as you are pushing the cuticles against the grain.

Each hair contains between 7-11 layers of cuticle. They are also translucent, which means they allow some light to pass through, which enables you to see the colour beneath. The cuticle can be damaged by harsh treatment. The cuticle has to be opened to allow chemicals to enter to the cortex. When this chemical treatment is finished the cuticle must be closed.

Structure of the Hair Root

Below the surface of the skin is the hair root, which is enclosed within a hair follicle. At the base of the hair follicle is the dermal papilla. The dermal papilla is fed by the bloodstream, to provide nourishment and produce new hair. The dermal papilla is very important to hair growth because it contains receptors for male hormones and androgens. Androgens regulate hair growth, and in scalp hair androgens may cause the hair follicle to become progressively smaller and the hairs to become finer in individuals who are genetically predisposed to this type of hair loss.