Hair Structure: The Facts

Hair Structure The diagram opposite shows a cross section of a hair shaft. Note the following: Hair is made from dead protein cells (keratin). A strand of hair has three layers: the cuticle (outer layer), the cortex (middle layer) and the medulla (inner layer). The medulla is a honeycomb keratin structure with air spaces within it.

• The cortex gives flexibility and tensile strength to hair and contains melanin (giving hair its colour). Without melanin, the partly hollow hair appears grey.
• The cuticle is made from 6 to 11 layers of overlapping semi-transparent scales (which make the hair waterproof and allow it to be stretched). Someone with thick, course hair will have more overlapping layers of cuticles that someone with fine hair.
• The hair structure is such that a healthy hair shaft will be very strong: it can stretch up to 30% of its length, absorb its own weight in water, and swell up to 20% of its diameter.