The Science of Hair

soulchild

New Member
This site is about Thermal Reconditioning, but it is very informative about hair. http://www.verticalsinhair.com/
I thought this was interesting.

WHAT IS KERATINIZATION, WHAT, IN FACT IS HAIR



“Let’s talk science”…chemical analysis of the hair reveals that each strand is composed of 70-85% protein. This protein is synthesized from 24 amino acids (To date, approximately 24 amino acids have been identified in the composition of proteins) that we obtain from protein sources in our diet. The strongest bond (and most important when it comes to straightening) is the cystine or disulfide bond. Any chemical service that alters the cortex may cause protein damage. Hair that is lacking protein will break easily. Natural color will look dull and lifeless and appear lighter in spots. Protein damage almost never occurs without moisture loss.



There are two main divisions of the hair, one above the surface of the skin and one below it. The portion of hair that we are usually most concerned about is called hair shaft, or keratin structure. This is the part of the hair that we see extending from the skin.



Hair, the way nature intended it to be. Beneath the scalp and under each and every hair fiber there is a living bulb. This bulb is composed of rapidly dividing cells that are genetically and biologically destined to become the principle components of the hair fiber. As these cells divide in the hair follicle, they are pushed upwards the scalp and change their shape, lose moisture, and become “cemented together” (cross-linked by the cystine/disulfide bonds) to form the hair fiber. This process of hardening is called Keratinization.



Keratinization. The hair fiber itself is primarily comprised of hardened cells (having produced in the bulb). These hardened cells are primarily comprised of proteins often called keratin (typically 93%). Thus the hair can be viewed as a “protein fiber”. In addition to the protein structure, there are traces of cellular material in the fiber including minerals, carbohydrates, and lipids (oils) in various forms, but by and large, the structural competency of the fiber depends on its protein (keratin) structure.



Moisture plays a part as well, since water can bind to this protein structure and the hair fiber may hold up to 16% of its weight in moisture in normal, healthy hair. The amount of coarse depends on the relative humidity. The higher the relative humidity, the more water the hair is able to hold. With these things in mind, it is therefore easy to see that much of the behavior of the hair is determined by the relative amounts of protein and moisture—thus, partially explaining why the hair may sometimes appear either dried out and brittle or soft and limp.



A closer look at the cuticle, cortex and medulla. Each individual strand is composed of three distinct layers which have different functions.



The cuticle or the outermost layer of the hair is a hard, shingle-like layer of over-lapping cells some 5 to 12 deep. It acts as a protective barrier for the softer inner structure and is said to be hydrophobic or water resistant. The cuticle is the first line of defense against all forms of damage.



When the cuticle is damaged, the hair appears dull, tangles easily, and has a rough texture. The more dehydrated and heat damaged the hair cuticle, the duller and frizzier your hair looks. Hair with cuticle damage will wet easily, which means that it absorbs liquids very fast— humidity and moisture can readily go in and out of the fiber causing the hair to frizz. This characteristic, “high porosity” can lead to further damage of the interior layers of the hair.



Moreover, as the hair gets older and longer, the cuticle layers wear away leaving hair susceptible to damage. The cuticle is extremely important to the cosmetic condition of hair not only because of its protective functions, but because it determines how the hair reflects light—its sheen or luster. It is also the only layer that we normally see or touch.



Cuticle damage can be caused by mechanical abuse during styling, and by chemical services. Bobby pins, barrettes, etc. may cause pinch marks, rubbing the hair and causing damage to the cuticle. Excess heat from blow dryers, hot irons, and hot rollers can weaken the cuticle layers, leading to split ends, and a dry, dull appearance of the hair. Moderately hot water and high water pressure will cause the cuticle to peel. Mechanical abuse such as brushing hair while wet, can cause extreme damage to the hair that is nearly impossible to repair.



The cuticle is the most resistant part of the hair. Cuticle proteins do not stretch and are more brittle than the cortical proteins. In fact, as the hair is stretched the cuticle will actually crack before the cortex breaks. It is important to teach “at-home maintenance” to prevent this damage from occurring.



If you stack some paper drinking cups inside one another, the top edges of the cup would represent the cuticle layers as they overlap. This type of overlapping arrangement is called imbrications, and they normally lie flat. The cuticle layers point toward the end of the hair shaft. They cannot be seen by the naked eye but they can be felt. If you slide your fingers along a dry hair from the end towards the scalp, the hair will feel sticky or rough—you are sliding your fingers against the cuticle and are lifting the imbrications/cuticle scales.



The cortex or centre portion of the hair strand lies beneath the cuticle. It looks like the spiral on the back of a notebook. One tiny fiber, a micro fibril and macro fibril will coil around other fibers to make a larger micro fibril. These fibers coil around each other to create the cortex. This spiral structure, much like a rope or yarn, makes the hair extremely strong and gives it elasticity.



The cortex is the main section of the hair, and it is here that we find the pigment granules that give hair its color. The cortex also contains the structure that gives hair its shape. This is the part of hair that we affect when we style it. When the hair is too curly or too straight, we chemically change the elements within the cortex (disulfide bonds) to add or remove curl “permanently”. The cortex also holds the hair’s water content. Because of this relationship, we might think of the cortex as springs arranged in a very thick protein/water “cement”. (Please take note)



The medullary canal is a hollow or partially hollow shaft which appears in some hair strands. It seems to have no effect with regard to the strength of the hair, but its presence or absence can alter the way in which the hair interacts with light. The exact function or purpose of the medulla has not yet been determined by scientists.



It is essential to have a competent hair structure. For example, if the cuticle is raised or abraded, chemical services may not respond satisfactorily, and the effects of humidity may compromise the longevity of the result on straightened hair. The structural competency or compactness of the cortex is important as well. If the cortex is disordered, the hair may not be able to withstand chemical services and it will cause the hair to become more disordered and/or break apart at various places in and along the fiber.



Shape and texture of hair. The shape of the individual hair shaft is generally related to the form of the hair. Straight hairs are usually round, wavy hairs are oval, and curly hairs are usually flat. These are only general rules and there are many exceptions. The shape of the hair is probably due to genetic or inherited factors.



In describing hair, we usually speak of its texture, porosity, elasticity and density.



The Texture of hair may be coarse, medium or fine, this is usually determined by the diameter of the hair—coarse hair has a large diameter. Another way of saying this is that coarse hairs are thick and fine hairs are thin. The texture and porosity are judged together in determining the processing time during a chemical service. Although porosity is the most important of the two, texture does have a part in judging processing time.



Porosity refers to the ability of hair to absorb moisture. The processing time for any chemical service depends much more on hair porosity than on any other factor. Coarse hair that is porous will process faster than fine hair that is not porous. The more porous the hair, the less processing time it takes, and a milder solution is required. Hair porosity is affected by excessive exposure to mechanical abuse such as blow-dryers, hot irons, sun, chlorine and continued use of harsh shampoos, colors, highlights and straighteners/relaxers. Hair that’s over-porous should not receive a chemical straightening treatment until the hair has been reconditioned, or removed by cutting.



Test the porosity of your hair. In order to test accurately for porosity, use three different areas: front hairline, in front of ears, and near the crown. Grasp small strands of dry hair and comb smoothly. Hold the ends firmly with the thumb and index finger of one hand and slide the fingers of the other hand from the ends towards the scalp. If the fingers do not slide easily, or if the hair ruffles up as your fingers slide down the stand, the hair is porous.



The more ruffles formed, the more porous is the hair. The less ruffles formed, the less porous is the hair. If the fingers slide easily and no ruffles are formed, the cuticle layer lays close to the hair shaft. This type of hair is least porous, is most resistant and will require a longer processing time.



Elasticity refers to the ability of the hair to stretch beyond its normal length and then spring back. Normal hair when wet can be stretched to about 40 to 50% of its normal length and return. Dry hair is not so elastic, it will stretch about 20 percent of its length and return to its normal position. When elasticity damage occurs, the cortex have been seriously disrupted or even destroyed to such extent that the elasticity of the hair is gone.



Hair elasticity is a very important factor to consider when giving a permanent straightener/Thermal Reconditioning. All hair is elastic, but its elasticity ranges from very good to poor. Hair with very good elasticity will produce resilient straightness. Hair with fairly good elasticity will produce slightly less than average resilient straightness. Hair with poor elasticity, also known as limp hair, will result in a very small amount of resiliency of straightness.



Caution: If the keratin molecular make up exhibits above average percent elongation/elasticity (allowing the fibers to stretch too much) the hair will not be resilient. Under No circumstances should chemical services be given when the hair is in this range.



Hair will change its elasticity from time to time. Usually, porous hair loses its elasticity faster than non-porous hair. This change may be temporary due to humidity and temperature, the type of shampoo used, the amount of hair spray/gels used, and drying action of wind and sun.



Signs of poor elasticity. When the hair is wet, it feels spongy, limp, tangles easily and stretches excessively without returning to its normal position. The most common cause of this serious condition is chemical services such as color, highlight, permanent straighteners either given improperly or too often, or both. Elasticity damage can also be caused by brushing wet hair—stretching the hair beyond its limit. The elasticity qualities of hair will determine the success/failure ratio of permanent hair straightening/TR.



Density refers to the amount of hair per square inch on the scalp. The hair is said to be thin, medium or thick depending upon how much hair there is. The average head of hair is approximately 120 square inches. There are nearly 1000 strands of hair per square inch.
 

Supergirl

With Love & Silk
Thanks for sharing
 

ChasingBliss

Well-Known Member
Very interesting, I especially am glad I read about bobby pins and barrettes causing pinch marks. I need to be careful of that.
 

Spagirl

New Member
If I weren't researching I would have missed this. Though I'm late, good info....thanks for sharing SoulChild!
 
Top