Hair develops wherever on the human skin with the exception of on the palms of our hands and the bottoms of our feet, yet numerous hairs are so fine they’re essentially undetectable. Hair is comprised of a protein called keratin that is delivered in hair follicles in the external layer of skin. As follicles deliver new hair cells, old cells are being pushed out through the surface of the skin at the rate of around six inches a year. The hair you can see is really a string of dead keratin cells. The normal grown-up head has around 100,000 to 150,000 hairs and loses up to 100 of them a day; finding a couple of stray hairs on your hairbrush is not really reason to get excited.
At any one time, around 90% of the hair on a scalp is developing. Every follicle has its own particular life cycle that can be affected by age, ailment, and a wide assortment of different variables.