It is really intriguing that hair, although composed of dead cells, keep growing. The secret of its growth lies in the hidden part of hair that remains under the skin.
Hair originates from a ring of dividing cells which later die out and contribute to its growth. At the base of the skin layer dermis? there are two distinct layers of skin, inner dermis and outer epidermis? the se-ed of growth is sown as a cluster of dividing cells in a follicle (small sac-shaped cavity).
These cells divide continuously depending on the nutrients and oxygen supplied by the skin tissue and blood vessels that surround the dividing cells. In the follicle, nascent cells move upward through the centre. The innermost cells die and harden into hair while the rest also die, giving rise to a double-layered hair sheath. Every dead cell adds to the length of the hair.
Just before it sprouts through the skin, hair is bathed in oil from the sebaceous gland which secretes oily matter. Hair growth may be affected by factors like nutrition, temperature, hormonal imbalance and diseases. The popular notion that frequent haircuts help hair growth is, of course, wrong.
Sources: The Telegraph (Kolkata, India)