Have you ever wondered what hair is made up of? In this post, we will examine the physical and chemical structure of hair.
Basic physical structure of hair
- The basic physical structure of the hair: cortex, cuticle and medulla
- The cortex is the main component of the hair and consists of moisture, melanin (pigment) and other elements.
- The cuticle is a chemically ‘resistant’ region surrounding the cortex in hair fibers. it consists of flat overlapping cells (scales) that surround the central fiber core. The cuticle cells are lined from the root to the ends pointing towards the ends, and can be compared to shingles on a roof. They can be 5-12 layers deep. One cuticle itself is made of several layers of cells. One can visualize the cross section of a cuticle as a lasagna. The cystine-rich proteins of the cuticle belong to the group of proteins called keratin-associated proteins.
Example of cuticles on a hair fiber
- The medulla cells are spherical and hollow inside and are bound together by a cell membrane material. These have been found to contribute negligibly to the chemical and mechanical properties of human hair fibers, and are sometimes not even present in hair.
Basic chemical structure of hair
- Human hair consists between 65%- 95% of protein, with the remaining constituents being water, lipids (fats, waxes etc.), pigments (for color) and other trace elements.
- Proteins are polymers of amino acids. The hair contains about 16 amino acids and derivatives thereof. It is particularly rich in the sulfur containing amino acids (and derivatives) such as cysteine, cystine, cysteic acid and methionine.
- These amino acids form the hard and resistant keratin protein structure of the hair through the strong sulfur-sulfur (disulfide) links, ionic interactions between opposite charges, non-ionic (Van der Waals) interactions and hydrogen bonding. See below:
- The water constituent in hair varies from person to person.
- The lipids of hair are mixtures of fats, waxes, glycerides etc. Their composition also varies from person to person, and is also age dependent.
- Pigments in the cortex of the hair are primarily melanin which gives the final color of the hair. The principal pigments of human hair are the brown-black melanins (eumelanins) and the less prevalent yellow/red pigments (pheomelanins). All humans have some pheomelanin in their hair but it’s the eumelanin that determines the darkness of the hair color. A low concentration of brown eumelanin results in blond hair, whereas high amounts of black eumelanin result in black hair. Note that levels of melanin can vary over time causing a person’s hair color to change.