Hair Chemistry And Structure

What Is Hair Made Of and How Does It Grow?

What Is Hair Made Of?

We will begin by defining the hair. Hair is composed primarily of proteins (88%). These proteins are of a hard fibrous type known as keratin. Keratin protein is comprised of what we call "polypeptide chains.” The word, polypeptide, comes from the Greek word "poly" meaning "many" and "peptos" meaning "digested" or "broken down".

In essence, if we break down protein, we have individual amino acids. Many (poly) amino acids joined together form a "polypeptide chain". Two amino acids are joined together by a "peptide bond", and the correct number of amino acids placed in their correct order will form a specific protein; i.e. keratin, insulin, collagen and so on.

The "alpha helix" is the descriptive term given to the polypeptide chain that forms the keratin protein found in human hair. Its structure is a coiled coil. The amino acids link together to form the coil and there are approximately 3.6 amino acids per turn of the helix (coil).

Each amino acid is connected together by a "peptide bond". The peptide bond is located between the carbon atom of one amino acid extending to bond with the nitrogen atom of the next amino acid. The best hair vitamins are typically great sources of amino acids.

hair chemistry and structure

The A Helix Coil

In the organization of a single hair, three "alpha helices" are twisted together to form a "protofibril". This is actually the first fibril structure of the hair. Nine protofibrils are then bundled in a circle around two or more to form an eleven-stranded cable known as the "microfibril".

These microfibrils are embedded in an amphorous unorganized protein matrix of high sulfur content, and hundreds of such microfibrils are cemented into an irregular fibrous bundle called a "macrofibril". These macrofibrils are grouped together to form the cortex (or the main body) layers of the hair fiber.

Packed dead cells surround these structures and are known as the cuticular layers of the hair. In the center of these structures lies the medullary canal, which is actually apart of the excretory system and houses any foreign debris, heavy metals, synthetics and medications that are thrown off by the body and eventually released through the canal.

Bonding in Keratin Protein

When the hair is in its normal unstretched state. It is referred to as A of alpha keratin. The original configuration of the hair is held in place by the bonding found in the cortex layers of the hair. As we stated earlier, keratin protein begins with an alpha helix building into protofibrils, microfibrils, macrofibrils, then cortex layers. The bonds in the hair are located within each and every alpha helix.

The Hydrogen Bond

The first bond we will discuss is the hydrogen bond. This bond is located between the coils of the alpha helix and is responsible for the ability of the hair to be stretched elasticity) and return back to its original shape. The hydrogen bonds allow us to change the shape of the hair temporarily with the aid of water.

These bonds are electrolytically controlled and are the most readily broken down and the most readily reformed. These bonds are responsible for approximately 35% of the strength of the hair and 50% of the hair's elasticity (some would argue up to 99.9% of the hair’s elasticity).

The Salt Bond

The salt bond is also an ionic (electrolytically controlled) bond formed by the electron transfer from the side chain of a basic amino group (an amino acid with an 00C- group) to the side chain of an acidic amino acid, i.e. NH3+. (This is two positive and negative charges attracting one another.)

This occurs in a position paralleled to the axis line of the rotation of the helix of the hair. The salt bond is responsible for approximately 35% of the strength of the hair and 50% of the hair's elasticity.

The Cystine Bond

The cystine bond also known as the disulfide bond, sulfur bond, or just S bond is formed by cross-links between cystine residues (amino acids) of the main polypeptide chains. This bond is perpendicular to the axis of the hair and between the polypeptide chains.

Because of its position in the hair, it is responsible for the hair's toughness or abrasion resistance. (It actually holds the hair fibers together.) These cross-links are frequent in the hair fiber, with maximum of frequency of one cystine bond every four turns of the alpha helix. This is what enables us to permanent wave the hair.

The Sugar Bond

The sugar bond is formed between the side chain of an amino acid having an OH group and an acidic amino group. This bond is also formed perpendicular to the axis of the hair. Because of its position, it gives the hair toughness but little strength (5%). Some moisture is contributed to the hair as a by-product of this bonding. Isn't hair fun?! :)

How Does Hair Grow?

Hair is actually dead material when it leaves it's root - otherwise it would hurt very much when your hairdresser works with his scissor. Most people know about this fact, but did you know about other facts:
  • On a normal scalp there are about 100-150 thousand hair fibers.
  • A blonde head of hair has usually much more fibers than red or dark haired heads.
  • Hair consists mainly of keratin, which is also responsible for the elasticity of fingernails.
  • A single hair has a thickness of 0.02-0.04mm, so that 20-50 hair fibers next to each other make one millimeter.
  • Hair is strong as a wire of iron. It rips after applying a force equivalent to 60kg, after it stretched itself for about 70%.

The root of a hair fiber sticks in a bag in the skin. The fiber is pushed out of this bag about 0.35mm per day, making an average growth rate of 1cm, or half of an inch, per month. The growth rate is however very much related to the individual person, his/her age, his/her diet etc.

Healthy hair has an average lifetime of 2-6 years. After a rest period of three months the single hair falls out, and a new fiber starts to grow out of the bag. The lifetime depends on circumstances and person, too. The lifetime of hair is responsible for the maximum of hair length you can have. Waist length hair takes about 6 years to grow out from a short hair cut, periodic trims included. If your hair has a lifecycle of 2 years, you will never achieve a nice waist length mane.

Baby hair begins to grow around the third month after conception within the womb of the mother. {Trichocysts} are first formed. They develop into hair follicles as the fetus grows, then become downy hairs several centimeters long when the baby is born. The total number of hairs is determined before the baby is born. After that, the number of hairs never increases. It just decreases. The number of hairs greatly varies for each person, from sixty thousand to one hundred and fifty thousand, and makes up one of natural characteristics of each person when they are born. We should take good care of our hair.

Human beings have about one million and four hundred thousand hairs on their body, with about four hundred and fifty thousand of them to be found above the neck!


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