A closer look at hair: It all begins here!
“Let’s talk science…” A closer look at hair will make you see beyond what you normally see and touch. See what the naked eye cannot see. After all, this is where the process of permanent wave, permanent hair straightening, Thermal Reconditioning, color, bleach and highlights begins; in the cortex (disulfide/cystine bond). It is here where the chemicals transform and rearrange the natural curl pattern of the hair from curly to straight, and vice versa.
What is keratinization, what in fact is hair! Chemical analysis of the hair reveals that each strand is composed of 70-85% protein. The strongest bond and most important when it comes to hair straightening is the cystine or disulfide bond. Any chemical service that alters the cortex may cause protein loss. Hair that is lacking protein will break easily. Natural color will look dull and lifeless and appear lighter in spots. Protein loss almost never occurs without moisture loss.
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 course 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 behaviour 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 defence 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 cause 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 lustre. 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 structure 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”.
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/TRd 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.
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/TR treatment until the hair has been reconditioned, or removed by cutting.
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.
Picture of Hair
The Proto-fibrils are connected to a single multi-strand cable known as the “Micro-fibril”. Hundreds of Micro-Fibrils form an irregular bundle of fibers, the “Macro-fibril”. The “cable strand” (fiber strand) is made up of many macro-fibrils. The “hair shaft” in turn is made up of these cable strands. The “medullar channel” containing the “medulla” is located at the centre of the hair shaft. Its structure has not been fully identified as yet. What is known is that the medullar channel is partially filled with a spongy hornlike substance displaying sizeable cavities in places. The space in between the fibrils (cable strands) and the scale layer (cuticula) is filled with “matrix” (filler substance). This filler substance consists of proteins, not in the form of helical spirals in this case, but in the form of amorphous (shapeless) substance. The hair shaft is surrounded by the “cuticula” (scale layer). This consists of numerous scale layers (up to 10), positioned on top of each other with their edges always pointing towards the end of the hair. Filler substance is located even between the scale layers, holding the individual scale layers together. The proportion of filler material has been enlarged in the diagram.