HOW HAIR GROWS
The portion of the hair that we can see is called the shaft. Each shaft of hair protrudes from its follicle, which is a tube-like pouch just below the surface of the skin. The hair is attached to the base of the follicle by the hair root, which is where the hair actually grows and where it is nourished by tiny blood vessels.
Like the rest of the body, hairs are made of cells. As new cells form at its root, the hair is gradually pushed further and further out of the follicle. The cells at the base of each hair are close to the blood supply and are living. As they get pushed further away from the base of the follicle, they no longer have any nourishment and so they die. As they die, they are transformed into a hard protein called keratin. So, each hair we see above the skin is dead protein. It is the follicle, which lies deep in the skin that is the essential growing part of the hair.
The thickness of each hair depends on the size of the follicle from which it is growing. At puberty in boys, hormones increase the size of the follicles on the chin, chest and limbs so that each hair becomes more thick and wiry. In the elderly, the follicles shrink and the hair becomes finer.
WHAT HAPPENS TO CAUSE BALDNESS?
Excessive hair loss can occur if any of the stages of hair growth becomes disrupted. For example, if follicles shut down (meaning that they stay in the resting phase and then shed the hair) instead of growing new hairs, there will be less hair on the head.
Another reason might be interference with the formation of new hair cells at the root during the growing phase; this occurs with some anticancer drugs. If follicles have been destroyed (as they might be by, for example, a burn or by some skin diseases), there will be baldness in that area.
An individual can also look bald if the hairs are growing but are so fragile that they break just as they emerge from the follicle, or if they are very small and thin.
