The Origin
of Hair

Topic 1: Structures of
the Hair

Topic 1 Activity

Topic 1 Summary

Topic 2: The Layers of the Hair

Topic 2 Activities

Topic 2 Summary

Topic 3: Chemical Composition of Hair

Topic 3 Activities

Topic 3 Summary

Module Assessment

Developer Bio

New Evaluation Form

Topic 3: Chemical Composition of Hair

Elements Found in Hair
Hair is made of protein which originates in the hair follicle.  As the cells mature, they fill up with a fibrous protein called keratin. These cells lose their nucleus and die as they travel up the hair follicle. Approximately 91 percent of the hair is protein made up of long chains of amino acids. The amino acids are joined to each other by chemical bonds called peptide bonds or end bonds. The long chain of amino acids is called a called a polypeptide chain and is linked by peptide bonds. The polypeptide chains are intertwined around each other in a helix shape.

There are various elements found in the hair and they are used to make amino acids, keratin, melanin, and protein.

The average compostion of normal hair is composed of  45.2 % carbon, 27.9% oxygen, 6.6% hydrogen, 15.1% nitrogen and 5.2a% sulphur.

The keratin found in hair is called "hard" keratin.  This type of keratin does not dissolve in water and is quite resilient. So what is keratin made from?  Keratin is an important, insoluble protein and it is made from eighteen amino acids.  The most abundant of these amino acids is cystine which gives hair much of its strength.

Amino Acids Present in Hair

Cysteine Aspartic acid
Serine Alanine
Glutamic acid   Proline
Threonine Isoleucine
Glycine Tyrosine
Leucine Phenylalanine
Valine Histidine
Arginine Methionine

Side Bonds of the Cortex

The middle layer of the hair, the cortex, is made up of millions of polypeptide chains cross-linked with each other by three different types of side bonds. The bonds that link up the polypeptide chains of the hair are hydrogen, salt and disulfide bonds. Hydrogen bonds account for one-third of the hair's strength. The hydrogen bond is a weak physical side bond that is easily broken by water or heat. Hydrogen bonds can be reformed by drying or cooling the hair. These bonds are very abundant in the hair.

Salt bonds are also weak physical side bonds that can easily broken by weak alkaline or acid solutions and changes in pH. These bonds can be reformed by normalizing the pH level of the hair.

Disulfide bonds are chemical side bonds. These bonds are stronger and fewer than hydrogen and salt bonds and cannot be broken by heat or water. A disulfide bond is joined to the sulphur atoms of two cysteine atoms to create cystine. Although the disulfide bonds are fewer than the physical bonds, they are the key factors in supplying the hair its' strength and durability.

The fourth bond is called van de Waal's Forces. This particular bond is based on the theory that atomic groups prefer an environment with other groups that have structures similar to theirs. This does not affect hairstyling services, students just need to know that they exist.

Hair Color Pigment

"Does She or Doesn't She?"

Often times when a person is asked to describe someone, the first thing they remember is the person's hair color. Hair color is a very unique and distinctive feature of a person. One of the most interesting aspects of hair is how hair gets its color.

Melanin is a pigment that gives color to the hair and skin. The melanin is produced by a group of specialized cells called melanocytes. These cells  exist near the hair bulb. They collect and form bundles of a pigment protein complex called melanosomes. The size, type and distribution of the melanosomes will determine the natural color of the hair.The type of melanin a person's hair has is inherited. The hair gets its color from two types of melanin that create the variety of hair colors we see.

Eumelanin is brown/black in color and is the most common type of melanin. This form of melanin gives color to hair shades from black to brown. Phaeomelanin is red in color and gives the yellow, ginger and red shades of hair their color.

Melanin is found in the cortex. Both eumelanin and phaeomelanin are present in the hair. What determines the hue we see is the ratio of eumelanin to phaeomelanin.

There are three basic factors that determine all the natural hair colors. They are:

a.  The thickness of the hair

b.  The total number and size of pigment granules

c.  The ratio of eumelanin to phaeomelamin

This is very important to remember when a colorist is changing the existing hair color of a client.  All three factors are important.  The density of pigment granules and the size of the granules varies from one race to another. Another important factor is the amount of cortex in coarse thick hair. The cortex is larger than in fine hair and therefore has a higher density of pigment. Blonde hair has fewer and smaller pigment granules of phaeomelanin. This makes blonde hair easier and quicker to lighten.

Gray Hair

The number of pigment granules naturally begin to decrease as a person ages. A person usually begins to gray between twenty-eight and forty years of age. The reason for this is that the melanocytes begin to slow down and produce less melanin. This is part of the natural aging process in humans. It is to be noted however, that some serious illnesses or emotional conditions may alsocause the hair to gray.

Glossary of Terms

Amino Acids – any one of a large group of organic compounds; the end product of protein hydrolysis.

Chemical bond – the force exerted by shared electrons that hold atoms together in a  molecule.

Disulfide links – bonds or linkages between polypeptide chains of the hair cortex.

End bonds – the chemical bonds that join amino acids to form the long chains characteristic of all proteins.

Eumelanin – one of two types of melanin, black /brown pigment.

Hydrogen bond (physical bond) – the molecular association between an atom of hydrogen and an atom of oxygen in the hair forming an electormagnetic bond. Gives strength and elasticity to hair and form to the hair when it is dry.

Keratin – a fiber protein characteristic of horny tissue; hair, nails, feathers etc. it is insoluble in protein solvents and has a high sulfur content.

Melanocyte – a pigment cell producing melanin in the hair bulb.

Peptide bonds – the joining together of amino acids

Phaeomelanin – naturally occurring red/yellow pigment in melanin.

Polypeptide bonds – bonds that link peptide chains together to form protein.

Polypeptide chains – amino acid chains joined together by peptide bonds; the prefix "poly" meaning many.

Sulfur bonds – sulfur cross bonds in the hair, which holds the chains of amino acids together; position determines curl present in the hair.