Biology, structure and function of hair.

Hair is much more complex than it seems. You can feel it at the root when it is moved or pulled. Protects your skin and traps particles like dust around your eyes and ears. You can express yourself through your hairstyle. If the hair is damaged, it will heal without scarring. Hair covers almost any surface of the human body.

This article provides an overview of the hair structure. Explain how it grows, what it is made of, and how it changes.

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How hair is formed

At 22 weeks gestation, babies already have all the hair follicles or holes in the skin where hair grows. This equates to about five million hair follicles, of which about one million are on the head and 100,000 on the scalp. This is the largest number of hair follicles you will ever have.

The follicles do not continue to grow throughout life. In fact, as we age, the number of hair follicles per square inch decreases as our bodies stretch and grow.

Hair structure

A lock of hair may seem simple, but it is actually one of the most complex structures in the body. Hair is made up of two separate structures. The hair follicle is the part under the skin and the hair shaft is what you see above the skin.

Hair follicle

The hair follicle is where your hair begins to grow and stays in place. It is a stocking-like structure that begins in the epidermis, the top layer of the skin. It spreads to the dermis, the second layer of your skin.

At the bottom of the follicle, a piece of tissue called the papilla contains small blood vessels ( capillaries ). They nourish the root of the hair so that it continues to grow. The follicle also contains the germinal matrix, the cells of which produce new hair.

The hair follicle at the root of the hair is a rounded structure deep in the skin. It surrounds the papilla and the embryonic matrix.

The bulb contains several types of stem cells that develop into specialized cells and can be renewed over a long period of time. These cells divide every 23 to 72 hours, faster than any other cell in the body.

The bulb also contains hormones that affect hair growth and structure at different stages of life, such as during puberty.

The follicle is covered with an inner and outer sheath that protects and shapes the growing hair. The inner sheath follows the hair and ends just before the opening of the sebaceous gland or sebaceous gland . The outer sheath extends to the gland.

The sebaceous glands produce sebum or oil, which is the body's natural conditioner. More sebum is produced during puberty, which is why acne is common during adolescence. With age, sebum decreases, resulting in dry skin.

The arrector pili muscle , a small bundle of muscle fibers, attaches itself to the outer sheath. When the muscle contracts, the hairs stand on end, also called goose bumps.


A hair follicle is a middle structure under the skin on which hair is formed. The follicle contains the membranes that make up the hair, the sebaceous glands that condition the hair, and the cells that produce new hair.

Hair shaft

The hair shaft is the part of the hair that we can see. As soon as the hair grows beyond the surface of the skin, the cells are no longer alive. It consists of three layers of keratin, a strengthening protein. These layers:

  • Inner layer: this is the medulla. The medulla is not always present depending on the type of hair.
  • Middle Layer – This is the cortex that makes up most of the hair shaft. Both the medulla and the cerebral cortex contain pigment cells responsible for hair color.
  • Outer Layer: This is the cuticle, which is made up of scales that are tightly packed into an overlapping structure that resembles a tile. Many hair care products are designed to smooth the cuticle by smoothing its structure.


The hair shaft is the part of the hair that we see above the skin. It can consist of three layers: the medulla, the cortex, and the cuticle.

Growth cycle

The hair on the scalp grows about half a millimeter a day. Individual hairs are always in one of three growth stages: anagen, catagen, and telogen.

  • Stage 1: The anagen phase is the hair growth phase. Most hairs are in this stage for three to four years. New hair pushes old hair that has stopped growing out of the follicle. The anagen phase of the eyelashes, eyebrows, hair on the legs and arms is very short: 30 to 45 days. Therefore, this hair is usually shorter than that of the scalp.
  • Stage 2: The catagen phase is a transitional stage and 3% of all hair is in this phase at any given time. It lasts two to three weeks. During this time, growth slows down, the outer root sheath shrinks and sticks to the hair root. It becomes a club of hair that stops growing.
  • Stage 3: The telogen phase is a resting phase that lasts for approximately three months. Represents 10% to 15% of all hair. During this phase, the hair follicle is at rest and the club hair is fully formed. When pulling out the hair, you will find dry white material at the root. The body loses 50 to 100 hairs per day.


There are three stages of hair growth. In the anagen phase, the hair on the scalp grows for three to four years. In the catagen phase, the hair slows down. In the telogen phase, hair stops growing and stays in place until new hair pushes it out.

How it takes shape

Some people have corkscrew curly hair, while others have thick, straight, and shiny hair. This appearance is due to the shape of the hair. Straight hair has a generally round circle. Curly hair strands are flat. The rounder the hair shaft, the smoother the hair will be. The flatter the shaft, the curlier the hair will be.

The cross-sectional shape of the hair also determines the degree of shine of the hair. Straighter hair is shinier because sebum from the sebaceous glands can travel through the hair more easily. In curly hair, sebum has a hard time moving through the hair, making it drier and dull.

As you age, your hair can change in color, texture, and thickness. You can even change some of your location, too much in some areas and too little in others.


The appearance of your hair is determined in part by its shape. If your hair has a round circle, it will be straight. If it is flatter than round, it will be curly.


Your hair is made up of a hair follicle and a hair shaft. The hair follicles in the skin contain living cells that allow hair to grow. The shaft, the part of the hair that we see, is made up of dead cells and is made up of three different layers. As hair grows, it goes through three phases before it falls out and grows back.

Get the word of drug information

You can keep your hair healthy by taking care of your overall health. Eating nutritious food is one way to improve your hair from the inside out. Talk to your doctor if you have questions about hair growth and how it might affect your health.

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