How Does Your Hair Grow?

Apart from appearance and physical protection of the scalp, your hair has many purposes and benefits. Being more complex than imagined, hair is also essential in transmitting sensory information and to create gender distinction and identification. Even in the fetal stage, hair follicles are useful. By the 22nd week, all hair follicles in the body are already formed. At this stage, about five million hair follicles are formed on the body.

About one million hair follicles are found in the head, with about 100,000 formed on your scalp. It is estimated to be the largest number of follicles an average human has. It is interesting to note that you do not generate or produce new hair follicles in your life. Another interesting thing you may have noticed about hair is that the general density of your scalp hair decreases as you grow into an adult. This need not indicate a reduction in the number of hair follicles, rather a spread out of the follicles since your scalp expands as your body grows.

What Is It Composed Of?

The human hair is comprised of four distinct parts i.e. the follicle,

cortex, cuticle and medulla. However, the follicle itself is made of many other parts. It is interesting to note that hair follicles are among the only two places in an adult human where stem cells are available.

On an average, your hair grows about six inches in a year and dies in the next four years. Your hair can also be divided into the follicle and shaft, the latter being visible over the scalp.

Hair follicle

The hair follicle can be defined as a tunnel like portion of the epidermal layer of the skin that extends all the way into the dermis. The structure of the hair follicle includes multiple layers with unique and separate functions. The base of your hair follicle is known as the papilla and contains blood capillaries that nourish your scalp and hair. The living part in your hair strands, known as the bulb, is located at the bottom of the scalp and surrounds the papilla. The cells existing in the bulb divide every 1-3 days and are significantly faster than

other cells in your body. It is this splitting of cells, which results in

hair growth, and can vary from person to person.

The hair follicle is surrounded by inner sheath and outer sheath that

protect and allow the hair shaft or strand to grow. The inner sheath ends below the oil glands, also known as the sebaceous gland or apocrine glands. The outer sheath on the other hand continues till the gland itself.

Arrector pili

A muscle named arrector pili is attached to a fibrous layer surrounding the bottom sheath at the lower part of the gland. When this muscle contracts; it results in the hair strands to stand up.

Arrectores pilorum (plural) are generally made of minute muscle fibers. The contraction of these muscles is involuntary and is often induced by cold weather. That is why you often experience goosebumps in cold weather or even air conditioned environments.

Sebaceous glands

The same function commands the sebaceous glands to secrete oil and

protect hair strands. The sebaceous gland is very important to maintain and protect hair health as it produces sebum, a substance

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