Hair Anatomy – Structure and How Does It Grow

It’s not hard to get beautiful hair. Be yourself to achieve it. This proverb means to say that whatever original hair you could have will be possessed only by your regular activities. However, in reality, we need an adequate amount of hair, irrespective of our daily activities. Some of them think that having long hair is some sort of style. However, hair growth is influenced by several factors. By changing certain ungood habits, one could protect their hair from hair loss. Before that, let’s understand the anatomy of hair, depicting its structure and hair growth.

Hair structure

Hair is a keratinous filament that projects out of the epidermis. Hair comprises dead and keratinized cells. The hair strands start at the epidermal depth of the dermis, known as the hair follicle. A hair shaft and a hair root are there for every hair. All the hair roots are piped to the hair’s other part, the arrector pili, which shrinks in response to nerve signals from the nervous system, thus making the hair stand up.

The hair root broadens to a round hair bulb at the hair’s base. The hair papilla inside the hair bulb supplies blood to the hair root. New and fresh hair cells are regularly produced in the hair bulb, which is nearer to the papilla.

Hair Follicle: A hair follicle, which is a sheath of skin and connective tissue, surrounds it and is also connected to a sebaceous gland. It is usually made up of many layers of cells that arise from the basal cells in the hair matrix and the hair root. The hair follicle’s wall contains three concentric cell layers.

Hair Shaft: The hair shaft is usually visible in hair that arises out of the skin. The hair shaft is a part of your hair and is not piped to the follicle, as much of this is exposed at the skin’s surface.

Cortex: The shape and structure of the cortex determine hair texture (straight or curly). It is present outside the medulla. The shape and structure of these layers are, in turn, decided only by the hair follicle’s shape. The cortex is a layer of compressed and keratinized cells.

Medulla: The central core of the hair is the medulla, and it is surrounded by the cortex.

Cuticle: The cuticle is usually covered by an outer, hard layer of keratinized cells called the cuticle. These layers are shown in a longitudinal cross-section of the hair follicle, although not every hair contains a medullary layer.

Hair Root: The rest of the hair parts, which are anchored in the follicle, lie below the skin’s surface, which is called the hair root. That is the hair root lies beneath the skin and projects down into the skin’s deeper layers.

Arrector pili: Every hair follicle is connected to a tiny muscle called the arrector pili, which helps make the hair stand up. However, most of the nerves terminate at the hair follicle, too. These nerves felt hair movement and could sense even the slightest draft.

The main function of this is to trap an air layer, which includes insulation. This is quite visible in humans as goose bumps and especially in animals, like cats.

Matrix: The hair root terminates in the hair bulb’s dermis and also adds a layer of mitotic cells, also called the hair matrix. The hair papilla is encircled by the hair bulb, which contains the connective tissue and other blood capillaries, along with the nerve endings from the dermis. The cells of the hair matrix extend to form layers of hair.

The basal layer of the epidermis, forming the layers of the epidermis, gets propelled to the surface as the dead skin on the surface sheds. The basal cells of the hair bulb get divided, and the cells are pushed outside the hair root and hair shaft while the hair grows. The projecting hair is usually transparent, with only its dark outline visible.

Hair Papilla: The hair papilla ensures that the blood is made available to the hair root, which lies inside the bottom of the hair bulb.

Hair Bulb: The hair root usually widens to form a round hair bulb at the base of the hair. New and fresh hair cells are constantly made in the hair bulb, which is very close to the hair papilla.

Root sheaths: the basal cells of the hair matrix in the middle are classified into cells of the inner root sheath. The root of the growing hair is encircled by cells of the internal root sheath, and it goes up to the hair shaft. The inner root sheath contains dark-staining nuclei.

At the base of the hair root, the basal cells form the outer root sheath. The external root sheath enclosing the hair root is an extension of the epidermis. It is more keratinous in the upper regions. The glassy membrane is usually very thick. The connective tissue sheath encloses the hair root, thus connecting it to the dermis tissue.

The outer root sheath is thicker than the inner root sheath, and it contains an oval of light-staining cells. These oval-containing cells surround the hair’s bottom and extend into the hypodermis.

Keratinization: The growth of hair starts with keratinocytes generated by the basal cells of the hair bulb. While the new cells accumulate at the hair bulb, the hair shaft will be sent through the hair follicle towards the surface. 

When the cells are pushed to the skin surface to form the hair shaft, the keratinization process is completed. The hair seen outside is completely dead and contains keratin. This is the reason why our hair does not have any sensations.

How does hair grow?

New cells are regularly produced in the hair bulb. These new cells adhere together and harden; as a result, a complete strand of hair is produced. As the newly hardened cells continue to link to the hair from below, they are then projected out of the skin. Through this process, the hair over your head slowly grows at a rate of about 1 cm per month.

Hair growing this way usually sheds and gets replaced by new hair. This process of hair shedding or replacement by new hair happens in three phases.

1. Anagen: The first phase, Anagen, is the phase in which the cells multiply quickly at the hair root, propelling the hair shaft up and out. This Anagen phase typically lasts 2 to 7 years.

2. Catagen: The catagen phase refers to a transition or adaptation from the growth of the hair follicles. The length of this phase is only 2 to 3 weeks.

3. Telogen: The telogen phase is the final phase. In this phase, the hair follicle rests as no new growth happens. This phase’s end is about 2 to 4 months long, during which another anagen phase starts.

A new hair follicle is generated by the basal cells in the hair matrix. This projects the old hair out due to the repetition of the growth cycle. The growth rate of the hair is 0.3 mm per day in the anagen phase.

More or less 50 hairs are lost and replaced each day. If the hair shed is more than the hair replacement, then it is called hair loss. Hair loss can occur due to the ageing process, dietary changes, or the impact of hormones. Facial hair, eyelashes, eyebrows, and body hair grow slowly.

The cross-sectional shape of the hair decides whether it is straight or curly. Round hair projects straight out of the skin. The oval-shaped cross-section results in curly hair.

Functions of hair

Hair performs many functions, like protection, thermoregulation, sensory input, and communication. On the head, hair protects your skull from the sun. Hair performs many functions, like protection, thermoregulation, sensory input, and communication. On the head, hair protects your skull from the sun. In the nose, ears, and around the eyes (eyelashes), the function of hair is to exclude dust particles like allergens and microbes, thus safeguarding the body. The hair in the eyebrows stops sweat and other particles from entering the eyes. When compared to the skin’s surface, hair is more sensitive to air movement or other disturbances in the environment.

The amount of melanin in the hardened cells determines the colour of the hair on the head. This could differ from person to person, and it may change gradually over a lifetime. When you grow older, the melanin amount typically reduces, and more air gets trapped inside the hair, thus losing its colour and becoming white. Based on a person’s original hair colour and the number of white hairs grown, their hair might change to grey or white.

What factors influence hair growth?

There are many factors that affect hair growth. Here are the factors that influence hair growth:

1) Ageing

Due to ageing, the hair might become less dense. You may lose your body and facial hair as you grow older. Then, the scalp might become visible, as most of the hair follicles stop generating new hair. The signs of baldness might be seen in men when they reach 30 years old. Some men are 50% bald at age 60.

2) Health

Generally, hair follicles are metabolically active in the body. Calorie and protein malnutrition could impact hair growth. Also, micronutrient deficiencies and other nutritional deficiencies impact both hair structure and growth.

3) Genetic and heredity factors

Genetic factors contribute to the length, colour, density, and texture of a person’s hair. Heredity disorders affect hair and other ectodermal structures as well.

4) Environmental exposure

Nowadays, many people are destroying trees, which naturally protect us from UV light. However, many environmental factors, like ultraviolet (UV) light, could cause damage to the hair structure. These environmental factors could make your hair less shiny, less elastic, or weaker than it was earlier.

5) Medications

Certain drugs or medications will have overdoses, or regular consumption might store some specific chemical compounds from those medicines in your body. Some drugs might cause hair loss by participating in the normal scalp hair growth cycle.

6) Pollution

Your scalp might be filled with environmental pollutants like dust, nickel, lead, smoke, arsenic, ammonia, polycyclic aromatic hydrocarbons (PAH), sulfur dioxide, nitrogen dioxide, and other volatile organic compounds due to exposure to environmental pollution. These pollutants might lead to oxidative stress, which might result in scalp irritation, excessive sebum secretion, redness, itching, dandruff, pain in the hair roots, and hair loss.

7) Growth hormone

If physical or mechanical forces damage the hair, or if the hair doesn’t get any necessary growth factors, then hair loss occurs. Usually, growth hormones will not cause any hair loss, as they trigger hair growth. The hair root undergoes destruction, also resulting in hair loss.

8) Smoking

Smoking causes the creation of DNA adducts, vasoconstriction, and free radical damage to hair follicles. Also, smoking enhances senescence and hormonal effects. This can result in less blood flow to your scalp and damage to the DNA of your hair follicles. So, smoking will lead to hair loss. To have a good amount of hair, strictly stop smoking.

9) Scalp conditions

There are many scalp conditions that could affect hair growth. Ringworm infections, alopecia areata, and dandruff could start hair loss and cause poor hair health.

10) Hair cosmetics

Along with nourishing the hair, processes like washing with chemicals and styling could damage the hair. Some cosmetic procedures and hair appliances could result in hair damage. Hair cosmetics might break the hair strands, thus resulting in hair breakage. Hair straighteners, blow dryers, flat irons, and curling devices insert heat into the hair and make it brittle.

11) The thyroid

The metabolism of hair follicle cells is affected by thyroid hormones. The amount of thyroid hormone could affect the brittleness of the hair.

12) Some health disorders

Autoimmune disorders like systemic lupus erythematosus, celiac disease, ulcerative colitis, and Crohn’s disease might alter cell metabolism and cause hair damage.

Conclusion  

Hair anatomy and its growth process are interesting to learn. The cuticle, the cortex, and the medulla are considered to be the main parts of hair. The hair follicle, hair shaft, hair root, arrector pili, matrix, hair papilla, hair bulb, and root sheaths are the other important parts of the hair. Hair growth takes place in three phases, namely, anagen, catagen, and telogen. The growth of hair is influenced by many factors, like genetics, healthy food, pollution, etc.

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