Some facts about hair
The hair root is the fastest growing organ in the body. The hair on the scalp, for example, grows at an average rate of 0.4mm a day (roughly 1/2 an inch a month).
Hair cells are formed in the matrix of the hair root that is situated in the deepest part of the hair follicle. Hair grows as a result of a continuous process whereby new cells form, mature and finally die, moving upwards as they do so.
The hair shaft, the only bit of hair that is visible, is composed of keratin, shares the skin's slight acidity and is entirely dead. In this and many other respects it much resembles the nail, another horny appendage of the skin.
The rate at which hair cells in the matrix reproduce is greater than every other tissue in the body except the bone marrow.
Such a highly active tissue is likely to react to illness or stress and if these are severe enough to interfere with the rate of cell division within the matrix, the result may be an immediate slowing down of hair growth.
There are four different types of hair. They are:
Scalp hair (discussed in detail on this site)
Eyebrow and eyelash hair, whose function is mainly protective.
Underarm and Pubic hair, which clearly marks out and embellishes the genital organs.
Body hair, whose main function is insulation.