Hair's Anatomy - Understand Those Hair Strands

THair Anatomy

 

This is something I should have discussed a long time ago, but hey, who knew I would still be going. I'm also going to wrench it up a notch with this discussion and start going into a bit more of the scientific angle, I am finding a lot of you are interested in the more technical talk and the more specific answers - so this will be a little more in-depth explanation of how the hair on your head is formed. I use these words so frequently, maybe if you understood them more completely it would help you relate what I am saying.

Hair is composed of protein that grows of cells originating within the hair follicle (why I stress the importance of protein in your daily diet). This is where the hair shaft begins. 

As soon as these living cells form, they begin their journey upward through the hair follicle. They mature in a process called keratinization. As these newly formed cells mature, they fill up with a fibrous protein called keratin, then move upward, lose their nucleus and die. You will see many products use that buzz word - keratin. I have performed many experiments with pure keratin, and truly did not notice any difference when it is added to the hair strand itself.  Compared to the tests with any oil by nature....the hair loves and adores anything oil based.. I even found some oil-based keratin from New Zealand that I played around for a few months and had a little luck, the problem ended up being if I wanted to use it in a product, it would cost me a fortune to get it delivered from New Zealand, so I had to scratch that idea. I tell you all this so you can watch for certain names in the thousands of hair products out there.

By the time the hair shaft emerges from the scalp, the cells of the hair are completely keratinized and are no longer living, but the root is still alive or it wouldn't grow. The hair shaft that emerges from the scalp is a non-living fiber composed of keratinized protein. Hair is a cylinder of impacted keratinized cells, I have included a simplified model of a single hair shaft (photo) and other various close-ups for you to refer to for the discussion of hair anatomy. A cross section of the hair shaft shows you the 3 major structures of a fully mature and keratinized hair. The central-most layer is the medulla, the next layer is the cortex and the outer layer is the cuticle.

MEDULLA - this section of the hair contains melanin granules and is present only in very thick terminal hair - generally only thick coarse hair contains a medulla( all male beard hair contains one) its quite common for very fine and blond hair to entirely lack a medulla. Notice the medulla is very deep and the very inside core of the hair, it is also the least important as far as hair care.

CORTEX - a fibrous protein core formed by elongated cells containing melanin pigment, about 90% of weight comes from the cortex. The elasticity and the hairs natural color begin here. Most of the changes to the hair shaft - such as those related to permanent color (oxidative coloring), semi permanent, chemical straightening, curling hair, permanent waving all occur in the cortex of the hair, the major component of the hair shaft. The cortex consists of elongated cells containing monofilament rich in cystine, this composition gives hair its great tensile strength.

CUTICLE - the integrity of the hair shaft is maintained by the cuticle. The cuticle consists of flattened cells along the hair shaft arranged like shingles on a roof. The overlapping is extremely tight, preventing damage to the underlying cortex. This is the part of the hair I refer to the most, I hope you can remember these scales, they are important in many references I will make over time. When the cuticle is intact, the scales are smooth, reflect light, and provide a shiny, healthy look to the hair! 

A healthy intact cuticle is the hair's primary defense against damage and this is the layer that really takes the most abuse. Lets just say > your cuticle hates your flat iron.

Hair is approximately 91 percent protein. 91% ! Now when I stress that PROTEIN -- PROTEIN -- PROTEIN must be burned into the back of your brain every time you go to eat, you can now see a hint of "why". The protein is made up of long chains of amino acids, which in turn are made up of elements. The elements that make up human hair are carbon, oxygen, hydrogen, nitrogen, and sulfur. These five elements are also the major elements found in skin and nails (remember > I find so many similarities in skin and hair - my basis for how THRIVEN was conceived) are often referred to as the COHNS elements. Table 8-1 shows the % of each element in normal hair.

The amino acids, the units of structure in protein, are linked together end to end like Mardi Gras beads. the chemical bond that joins amino acids to each other is called a peptide bond . A long chain of amino acids linked by peptide bonds is called a polypeptide chain. Polypeptide chains intertwine around each other in a spiral shape called a helix.
The 4 most important hair characteristics that affect its function and appearance are density, elasticity, porosity and texture. Which is an entire Department or D-E-P-T its initials.

DENSITY : measures the number of individual hair strands on one square inch. It indicates how many hairs there are on a persons head. Hair density can be classified as low, medium, or high ( or thin, medium, or thick-dense). Hair density is different from hair texture in that different individuals with the same hair texture can have different densities and vice-versa. Some individuals may have coarse hair texture (each hair has a large diameter), but low hair density ( a low number of hairs on the head). Others may have fine hair texture (each hair has a small diameter) but high hair density ( a high number of hairs on the head). Hope that isn't too confusing, this is an important fact for those of you working with me on hair color consultations.     The more info like this that you can break down and explain to me the more "right-on" we will get with your own personal hair color formulation.

The average hair density on 1 head > about 2,200 hairs per square inch. Hair w/ high density ( thick or dense hair) has more hairs per square inch. The average head of hair contains about 100,000 individual hair strands. the number of hairs on the head generally varies with the color of hair. Blondes usually has the highest density and redheads ( boo-hoo) have the lowest.

POROSITY: If only I could stress the importance of this characteristic, I would be able to assess some of your hair so much easier. Porosity is the ability of the hair to absorb moisture. The degree of porosity is directly related to the condition of the cuticle layer therefore healthy hair with a compact cuticle layer is naturally resistant to penetration. Porous hair has a raised cuticle layer that easily absorbs water.

Hair with low porosity is considered resistant (see photo) . Chemical services performed on hair with low porosity require a more alkaline solution than those on hair with high porosity. Alkaline solutions raise the cuticle and permit uniform saturation and processing.

Hair with average porosity is considered normal (see photo) . Chemical services performed on this type of hair will usually process as expected, according to texture, which is why if I know this about your hair I can gauge more accurately your outcome, so I encourage all of you to figure each of these characteristics out about your own hair, its good information to have for life, I feel.

Hair with high porosity is considered overly porous and is the results of previous over processing (see photo).Over porous hair is damaged, dry, fragile and brittle. Chemical services performed on overly porous hair require less alkaline solutions with a lower pH. This will help over processing.(Yes, I realize we need to go into the whole entire pH story, which we will very very soon - it is hard to decide whether to start with the chicken or the egg in explaining this - its ALL necessary).

The Texture of the hair is not an indication of its porosity. Different degrees of porosity can be found in all hair textures. Although coarse hair normally has a low porosity and is resistant to chemical services, coarse hair can also have high porosity as the result of previous chemical services.

Here is a nifty trick . . you can check porosity on dry hair by taking a strand of several hairs from 4 different areas of the head ( the front hairline, the temple, the crown, and the nape). Hold the strand securely with one hand while sliding the thumb and forefinger of the other hand from the end to the scalp. If the hair feels smooth and the cuticle is compact, dense and hard, it is considered resistant. If you can feel a slight roughness, it is considered porous. If the hair feels rough, dry or breaks it is considered overly porous.

ELASTICITY Is the ability of the hair to stretch and return to its original length without breaking. Hair Elasticity is an indication of the strength of the side bonds that hold the hair's individual fibers in place. Wet hair with normal elasticity will stretch up to 50% of its original length and return to that length without breaking. Hair with normal elasticity holds the curl from wet sets and permanent waves without excessive relaxing.

Hair with low elasticity is brittle and breaks easily. Hair with low elasticity may not be able to hold the curl from wet setting, thermal styling ( curling irons ) or perms. Hair with low elasticity is the result of weak side bonds that usually result from over processing. Chemical services performed on hair with low elasticity require a milder solution with a lower pH, that solution minimizes damage and helps prevent additional over processing.

Check elasticity on wet hair by taking an individual strand from four different areas of the head ( the front hairline, the temple, the crown, and the nape). Hold a single strand of wet hair securely and try to pull it apart ( see photo - elasticity). If the hair stretches and returns to its original shape without breaking, it has normal elasticity. If the hair breaks easily or fails to return to it original length then it has low elasticity.

TEXTURE is the thickness of diameter of the individual hair strand. Hair texture can be be classified as coarse, medium, or fine and differs from individual to individual (see all photos). Hair can also vary from strand to strand on the same person's head! It is not uncommon for hair from different areas of the head to have different textures. Hair from the nape (back of the neck), crown, temples, and front hairline of the same person may all have different textures - just to confuse matters even more.

Coarse hair texture has the largest diameter. It is stronger than fine hair, for the same reason that a thick rope is stronger than a thin rope. Coarse hair also has a stronger structure. It usually requires more processing than medium or fine hair and may also be more resistant to that processing. It is usually more difficult for hair lighteners, hair colors, permanent waving solutions, and chemical hair relaxers to penetrate coarse hair, so that is why this subject is relevant in the overall scheme of hair .

Medium hair texture is the most common and it is the standard to which other hair is compared. Medium hair is considered normal and does not pose any special problems or concerns.

Fine hair has the smallest diameter and is more fragile, easier to process, and more susceptible to damage from chemical services than coarse or medium hair. Finer hair is hair that one should choose the least amount of time for chemical services possible, as a safeguard. With bleach you will be leaving it on quite a bit less than coarse hair. See why these characteristics are so very very important ? If you figure them out about your hair you can take them into account when coloring your hair the first time and therefore you can avoid any disasters from happening.

Hair Texture can be determined by feeling a single dry strand between the fingers. Take an individual strand from 4 different areas of the head -- the front hairline, the temple, the crown, and the nape -- and hold the strand securely with one hand while feeling it with the thumb and forefinger of the other hand. With a little practice you will be able to to feel the difference between coarse, medium and fine hair diameters.

These 4 major characteristics of the hair shaft, Density, Elasticity, Porosity & Texture (dept.) -- will affect the overall permeability of hair to chemicals and liquids of all type.Therefore how shampoo affects it as well.

Texture and Porosity are judged together in determining the processing time. Although porosity is more significant, texture is also important. Fine hair, having a small diameter, will become saturated with wave lotion more than hair with a large diameter if both are equally porous. Coarse hair that is very porous, however will process faster than fine hair that is not porous. The hair texture will also contribute to its elasticity. The stronger the hair shaft, the greater its elasticity.

Whew! that was a mouthful and page full but its something I have wanted to get said. So I am glad it finally is. This is just the beginning of how the hair structure pertains to shampoos,color and hair care products, which is all forth coming so just hang on.

Killer Chemist