Human hair consists of:
● Hair shaft, the part that sticks out from the skin’s surface
● Root, a soft thickened bulb at the base of the hair
● Follicle a sac-like pit in the skin from which the hair grows
○ At the bottom of the follicle is the papilla where the actual hair growth
happens. The papilla contains an artery that nourishes the root of the hair.
As cells multiply and make keratin to harden the structure, they’re pushed up
the follicle and through the skin’s surface as a shaft of hair.
Some 18 amino acids can be found in the hair, such as proline, threonine, leucine and
arginine. Keratin is particularly rich in cysteine (a type of sulfurated amino acid), which
forms disulfide bonds between molecules, adding rigidity and resistance to the entire
structure.
The hair’s structure can be divided into 3 distinct parts:
- Medulla: innermost layer of the hair shaft, composed of an amorphous, soft, oily substance
- Cuticle: thin protective outer layer that contains the nourishing portion essential to hair growth. It is highly keratinized, composed of cells shaped like scales that are layered one over the other, measuring about 60 micrometers long and about 6 micrometers wide.
- Cortex: main component of the hair, containing long keratin chains that add elasticity,suppleness and resistance to the hair. The cells of the cortex are joined together by an intercellular cement rich in lipids and proteins. Each cell is composed of bundles that lie in the direction of the hair length: these are macrofibrils which are made up of microfibrils, which in turn contain protofibrils.