The number of hair that grows on the scalp, which grows at about ½ inch (13 mm) a month, averages at about 100,000-150,000. The hair shaft is composed of a protein called keratin, the cuticle, the medulla, and the cortex.
The cuticle is the thinnest layer. It is transparent and consists of overlapping scale-like cells. It protects the cortex from chemicals.
The medulla is the core of the hair shaft and contains soft keratinised cells, which is key in helping to give hair its elasticity.
The cortex is the middle layer. It contains 75% to 80% of the hair’s protein structure. It is also where moisture and melanin (natural pigment) are held.
Hair is formed by cell division at the base of the follicle, and is a part of a cycle of growing, resting, and shedding. The growing cycle can be as short as 2 years and as long as 10!
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