The Anatomy of Hair: everything you need to know about hair.

Aug 24, 202419 min read

Written by: Zenani Sizane

The mane thing. Some people wear it up, while others wear it down. It comes in a variety of forms, styles, and sizes. The only part of our bodies capable of telling or concealing a tale. This is one of our few body organs that we pay close attention to; we care whether we lose some or gain more, we enjoy receiving comments on it, and we care whether others notice.

If you haven't figured it out yet, we're talking about your lovely hair, and in this blog post, we'll go over everything about it, including what it is, the various types of hair, how it grows, and how to care for it. We want you to know everything there is to know about your hair so you can care for it properly.

The Anatomy of Hair: What is hair?

Our hair is one of our most distinctive traits; for many people, it is part of their appearance and a reflection of their individuality. Our hair is as unique as we are, and everyone's hair differs for many different kinds of reasons, including genetics, ethnicity, and environment. Every person's hair can tell you a story about who they are and where they came from, and because our hair is such an important part of who we are, we need to have a basic understanding of Hair Anatomy, as this will help us understand the inner workings of our hair, allowing us to better care for our beautiful hair, which is essentially the "main attraction" to our being. In this article, we will learn about hair design, growth cycles, types, and more.

Hair is a characteristic of the mammal class (which includes humans); practically our whole body is covered in hair follicles, with the exception of the palms, soles of the feet, and lips. It is estimated that humans have 5 million hair follicles, approximately 100,000 of which are on our heads. Hair has various purposes, including protection from external elements and thermoregulation, the production of sebum, perspiration, and pheromones, an impact on social relationships, and a source of stem cells.

The hair on different places of our bodies serves distinct functions. Our nasal channel hair filters pathogens: our brow and eyelash hair keep sweat and dust out of our eyes; and body hair stands up when it's chilly, functioning as an insulator and keeping a layer of warm air near to our skin.

Hair is far more intricate than it appears, it is made up of keratin, a strong fibrous protein, and skin-like cells. Hair is made up of two basic parts: the follicle and the shaft. In the following sections of the article, we will explore the follicles and shafts and how they contribute to strong, healthy hair.

The Follicle

The hair follicle is a little organ that is the living component of our hair. Hair grows from a single follicle, and each hair follicle has its own blood nerve and muscle supply, known as the bulb, which is located at the junction of the deep dermis and hypodermis. Our genes control follicle location, distribution, and type; you are born with a set number of follicles that cannot be changed, and the size of your follicle determines hair thickness. The shape of the follicle influences whether your hair grows straight, curly, or coily.

The follicle is located in the skin and is attached to a little muscle known as the arrector pili, which permits our hairs to stand up or lie flat. The blood vessels carry nutrients to the follicle. Nerves attach to the follicle and provide a sense of movement, such as a draft in the air. Furthermore, each follicle contains a sebaceous gland, which generates sebum to moisturize and preserve the skin, scalp, and hair.

An inner and outer sheath surrounds the follicle, protecting and shaping it as it grows. The inner sheath follows the hair and finishes immediately before the opening of the oil gland, also known as the sebaceous gland. The outer sheath extends all the way up the gland.

The sebaceous gland generates sebum, or oil, which is the body's natural conditioner. Puberty causes greater sebum production, which is why acne is common during adolescence. Sebum production declines with aging, leading the skin to become dry. The blood arteries that surround your follicles transport the nutrients your hair requires to thrive; this is one of the reasons why your diet is so important for healthier hair growth and strength.

The papilla (the bulb) is located at the base of your follicle, on the dermis (the deeper layer of your skin), and it includes tiny blood vessels (capillaries) where the majority of hair growth occurs; these nourish the hair root and keep it glowing. The follicle also houses the germinal matrix, which is where cells generate new hairs. The nerves and muscles around your follicles provide your hair with tactile characteristics, allowing you to feel even the tiniest movement; it is the muscles that contract and give you goosebumps when you are cold or frightened.

The Hair Bulb

The hair bulb is a structure composed of actively growing cells that eventually form hair. Cells divide constantly in the lowest half of the bulb and push upward, gradually hardening. The bulb of the follicle contains an array of cells known as the hair matrix: epithelial cells that harden to form a strand of hair; keratinocytes (cells that synthesize keratin), which eventually cover the hair shaft in keratin; and melanocytes, melanin-forming cells that give our hair pigment. The cells beneath the epidermis gradually push the strand of hair upwards, forming the shaft.

The Hair Shaft

Each hair has a shaft and a hair root. The shaft is the visible part of the hair that sticks out of the skin and is non-living. The hair root is in the skin and extends down to the deeper layers of the skin. It is surrounded by the hair follicle, which is a sheath of skin and connective tissue, that is also connected to a sebaceous gland.

The hair shaft is primarily composed of keratin, a fibrous protein that provides hair with strength and structure. Keratin is made up of amino acids bonded together by two types of bonds, with which you may have previously interacted without realizing it. The first is the disulphide bond, which is strong and determines your hair type (straight, curly, wavy, or coily). Disulphide bonds are difficult to break naturally, and typically require severe heat or chemicals.

You may have chemically broken these bonds if you have ever had your hair relaxed or permed. You broke the bonds to change your hair shape. The second kind is the hydrogen bond, which is much weaker, it can be broken by wetting your hair or heating it, which allows hair to be styled with a hair dryer or curling iron.

The hair shaft consists of three layers:

The three inner layers become the hair; it is made up of the medulla, the cortex and the cuticle. The medulla is not always present in hairs with a thinner diameter.

The Medulla (the inner layer)

The medulla is the central part of the shaft, and it is composed of amorphous, soft and greasy substances. It contains large, keratinized cells as well as air pockets, a variation of which gives hair its porosity. Depending on the type of hair, the medulla is not always present.

The Cortex

The cortex consists of melanocytes and keratinocytes (melanin and keratin producing cells, respectively). The cortex is the main component of the hair, where we find long chains of keratin, which are held together by disulphide and hydrogen bonds and that give the hair its elasticity, flexibility and resistance. The cells of the cortex are linked together by an intercellular cement rich in lipids and proteins. Each cell is made up of bundles oriented in the direction of the length of the hair. The health of the cortex depends largely on the integrity of the cuticle protecting it.

The role of melanocytes and keratinocytes

The hair cortex also contains melanin. It is produced by specialized cells called melanocytes, melanin is a pigment responsible for hair color, located near the hair bulb, melanocytes inject their pigments into the keratinocytes of the developing hair shaft. The color thus lasts throughout the hair cycle, from its genesis to its end, when the hair falls out.

The Cuticle

The cuticle is made up of hair-like, overlapping keratinized cells that protect the inner layers. The cuticle is a thin, protective covering that contains the nourishing portion necessary for hair production. It is highly keratinized and made up of scale-like cells that overlap. It retains your hair in the hair follicle with a Velcro-like adhesive.

It also reduces the flow of water (moisture) into and out of the underlying cortex. However, chemical reactions and weathering have the potential to raise the cuticle and disrupt this balance. A healthy cuticle has smooth and flat cells that help our hair appear lustrous and in good condition while protecting the inner layers from injury. Many hair conditioning solutions are designed to clean the cuticle while smoothing its structure.

How does your hair grow?

By week 22 of pregnancy, newborns have developed all of their follicles, or openings in the skin where hair grows. This totals approximately five million hair follicles, with one million on the skull and one hundred thousand on the scalp. This is the highest amount of hair follicles you'll ever have. Follicles do not continue to grow throughout life. In truth, as we age, our bodies stretch and grow, resulting in fewer hair follicles per square inch.

A strand of hair may appear simple, but it is one of the body's most intricate systems.

Hair grows from the follicle, and a small vessel that enters the hair shaft provides the hair with all of the nutrients it needs to be healthy, including amino acids, minerals, and vitamins. Hair consists of 18 amino acids, including proline, threonine, leucine, and arginine. Keratin contains a high concentration of cysteine, a sulfur amino acid that creates disulfide bridges between molecules, giving it overall rigidity and strength.

New cells are constantly forming in the hair bulb, these cells stick together and harden. The full strand of hair develops from a group of hardened hair cells. Because new hardened cells keep attaching to the skin. In this way, a single hair on your head grows at a rate of about 1 cm per month. Facial hair, and especially eyelashes, eyebrows, and body hair, grows at a slower pace.

Glands surround the hair shaft, the most important being the sebaceous gland, which generates sebum, the hair's natural lubricant. The pores on the scalp expel perspiration produced by the sweat glands.

Hair's cross-sectional shape determines whether it is straight or curly. Round hair grows straight from the skin. The more oval-shaped the cross-section, the curlier the hair. Hair color is determined by the amount of melanin in the hardened cells. This varies from person to person and changes throughout one's life. As people age, their melanin levels decline, and more air becomes trapped inside their hair, causing it to lose color and turn white. The hair on someone's head can be gray or white, depending on their original hair color and the number of white hairs that grow.

Healthy hair can stretch up to 50% of its length, absorb its weight in water, and swell up to 20% of its diameter. A single scalp of hair can hold a weight of 100 g, and an average head of hair twisted together can support 23 tons.

As long as new hair cells continue to grow in the hair bulb. The hair continues to grow longer. This growth phase is also called the anagen phase. At any point in time, about 90 percent of a person’s total amount of hair is in the growth phase.

The hair growth cycle

It is useful to understand the hair growth cycle in order to recognize and understand many of the problems you encounter with your hair. Because hairs continue to enter the resting phase and then fall out, we are constantly losing hair. A healthy adult may lose about 70 to 100 hairs on their head per day. Although new hairs are always growing and being replaced, this natural hair loss is not always noticeable.

The rate of hair loss may increase noticeably if the hair roots are damaged during the growth phase or if a lot of hairs go into the resting phase at the same time. If no new hair grows and replaces the old one, that part of the skin becomes bald, this type of hair loss is referred to as alopecia- regardless of how large the bald spot is or whether it affects the scalp or body hair.

Depending on where on the body a hair grows, the growth phase will last longer or shorter. For instance, the growth phase of hair on your head can last several years, so it can grow to over a meter in length if you don't cut it. The growth phase is especially short for eyelashes, eyebrows, nasal hair, and ear hair.

At the end of the growth phase, the hair root separates from the papilla. Then a transitional phase called the catagen phase starts, lasting about two to four weeks. When the hair has separated completely from the papilla, the supply of blood is cut off in the final resting phase, which is also called the telogen phase. The hair is gradually pushed out of the skin and eventually falls out. The telogen phase can last for several months. New hair cells then start to multiply at the base of the empty hair follicle to form new hair, and the growth phase of the hair growth cycle starts all over again.

The hair on your scalp grows less than half a millimeter a day, and from the time each hair starts to grow to the time it falls out many years later, it cycles through four stages:

The first three phases cover the growth and maturation of hair and the activity of the hair follicles that produce individual hairs. Each phase has its own timeline, which can be different by age, nutrition, and overall health. During the final, or exogen phase, “old” hair sheds, though usually new hair is getting ready to take its place.

The Anagen Phase - Growth phase

During the anagen phase, your hair follicles are pushing out hairs that will continue to grow until they are cut or until they reach the end of their lifespan and fall out. At any time, about 90 percent of the hairs on your head are in the anagen phase.

The Catagen Phase - Transition Phase

The catagen phase starts when the anagen phase ends and tends to last about 10 days or so. During this chapter, hair follicles shrink, and hair growth slows. The hair also separates from the bottom of the hair follicle yet remains in place during its final days of growth. 5% of the hairs on your head are in the catagen phase at any given time.

The Telogen Phase - Resting Phase

The telogen phase typically lasts around three months. An estimated 10 to 15 percent of your scalp hair is in this phase. Hairs don’t grow during the telogen phase, but they don't usually fall out either. The telogen phase is also when new hairs start to form in follicles that have just released hairs during the catagen phase. Some health experts consider the telogen phase and the shedding phase as one phase, but some scientists have divided this stage into two parts: the telogen phase and the exogen phase.

The Exogen Phase - Shedding Phase

The exogen phase is essentially an extension or a part of the telogen phase of hair growth. During the exogen phase, hair is shed from the scalp, often helped along by washing and brushing. Losing 50 to 100 hairs per day during the exogen phase is normal. During the exogen phase, which can last about 2 to 5 months, new hairs are growing in the follicles as old hairs fall away.

How hair gets its shape and the different hair types

Now that we have a better understanding of how our hair grows, its different layers and also the different phases it goes through, it is also important to understand our hair’s appearance, how it gets its shape and grows, as this will give you a better understanding of how to approach your hair care routine.

Our hair is unique as we are, everyone’s hair is different based on their genes and ethnicity, but it also differs based on diameter of the shaft, curliness, strength, color and density/ porosity. Each of these can differ, giving us our unique hair type. Some people have curly corkscrew hair, while others have thick, straight shiny hair. This appearance is due to the shape of hair. Straight hair has mostly circular circumference. Strands of curly hair are flat. The more circular the hair shaft, the straighter the hair and the flatter the hair shaft the curlier the hair.

We've learned that hair is made up of three layers: the inner medulla, central cortex, and outer cuticle. Pictures of the hair shaft typically show a cylindrical shaft, but our hair is actually elliptical in shape, similar to the orbits of the planets around the Sun.

The degree of ellipses determines the curliness of our hair. And the ellipses of the hair shaft are determined by the particular cell arrangement on the cortex. Otho-cortical cells are on the side, outside of the coil, and para-cortical cells are on the inside (concave) of the coil.

This cross-sectional shape of hair also determines the amount of shine that the hair has. Straight hair is shinier because sebum from the sebaceous gland can easily travel down the hair. With curly hair, the sebum has trouble traveling down the hair, making it look drier and duller. As you get older, your hair can change color, texture and thickness. It can even change some of its location, with too much in some areas and too little in others.

Ratios of the ortho-and para cells define the curl pattern, number of curls per unit length, as well as the curl definition. Hair with a high ratio of ortho-to para-cells is straighter and has more cylindrical shaped shafts, while hair with a higher number of para-to ortho-cells is curlier and has more elliptical shaped shafts.

And that’s why some people have wavy, curly or coily hair and others have straight hair: the degree of curliness has several knock-on effects on the overall hair type: stiffness, moisture and porosity.

That being said, there are several factors that play a part in determining your hair type. The hair typing system was developed by celebrity hair stylist Andre Walker. Who developed the hair typing system in the 1990s to help people understand their hair better in order to care for it in the way it needs.

In order to determine your hair type, there are several factors you need to determine to have a full scope of how your hair behaves, because your hair type is more than just being Straight 1A hair, you also need to determine the porosity, density, moisture and stiffness of the hair, as they all play an important part in what you need to care for your hair.

Here are the factors that help you determine your hair type:

Stiffness

Hair stiffness is determined by the diameter of the hair shaft as well as the degree of coiliness.

Moisture

Curly hair types tend to have a lower moisture level than straight hair types, as sebum moves slower down a winding hair shaft than a straighter one. This leads to straight hair types typically experiencing more oiliness, while curly hair types are typically drier and require more moisture-but not too much moisture or it may strip the strand of protein and cause damage.

Porosity

Hair porosity refers to the hair’s ability to absorb and retain moisture. Highly porous hair swells during washing as it takes in water, but since it is a poor moisture retainer, it loses the water and dries quickly. This can lead to protein loss, so if you have very porous hair, it may be a good idea to add some hydrolyzed protein into your products. Hair with low porosity means it is hard to absorb moisture, but once it is there it retains it well.

Hair porosity is influenced by the degree of curliness; straight hair tends to be less porous, while wavy, curly or coily hair tends to be more porous, but of course variations and deviations can occur here.

Density

Hair density refers to the number of hairs on your head. If you can’t see your scalp clearly, you probably have dense hair. If you can see your scalp even without parting your hair, you probably have low density hair.

Your hair’s density can be affected by a number of factors, including stress, hormones, during pregnancy or menopause and nutrition. It is a good idea to take stock of the products you are using if your hair density has changed.

The Different Hair Types:

The hair type system was developed according to the hair properties we have discussed above:

Straight, wavy, curly, and coily is numbered 1,2,3 and 4 respectively.

Hair texture from fine to medium to coarse is lettered A, B and C respectively and these categories are combined.

Disclaimer: the hair typing system is not the only way to define your hair’s curls of texture, but it is one tool to help us choose the best products to care for our hair.

Straight Hair Type

Straight hair or type 1 hair is straight, fine and completely devoid of kinks, curls and frizz. Straight hair is soft to the touch and shiny as a result or the straight shot of natural oils from the root to the tip of the shaft can result in an oil buildup that makes type 1 hair appear greasy and weighed down if not properly treated.

The subcategories of type 1 hair are: type 1a, 1b and 1c. Type 1a is pin straight, wispy and particularly shiny with an inability to hold curls or waves. While 1b hair loss has more body than type 1a hair, it remains straight and shiny. Lastly, 1c has a body with a slight bend and less wisp and shine than type 1a and 1b.

Wavy Hair Type

Type 2 wavy hair is often mistaken for type 3 curly hair, but these two hair types are vastly different in appearance and structure. Wavy hair is most easily identified as “influencer hair” with loose ‘S’ waves that cascade from just under the roots to the tip of the hair shaft. Type 2 hair is largely influenced by temperature fluctuations; the heat of the summer may emphasize your waves and enhance frizz while the cold, dry temperature of the winter months can leave your waves flat and tamed.

In addition, wavy hair is often balanced with regards to oil production making it neither too oily nor too dry; characteristic, paired with the natural bend in the hair shaft, allows for easy styling with all type 2 hair.

Type 2A hair has a barely there, tousled ‘S’ wave with fine strands that are easy to straighten. As with type 1 hair, type 1 hair, type 2a hair is dispersed oil more efficiently from root to tip, which requires more frequent washing to avoid a greasy look. Type 2b hair is slightly more tousled with a more defined ‘S’ wave and medium thick hair structure. This subtype has more frizz by nature and moves the body for a beach wave aesthetic. Type 2c hair is most often confused with type 3 curly hair; this wavy hair subtype is coarse with thick structure and defined ‘S’ waves that closely resemble a loose curl. Type 2c hair is more difficult to style than other type 2 hair.

Curly Hair Type

While type 2c wavy hair and curly hair are often confused, curly hair and coily type 4 hair are also incorrectly grouped together. Type 3 curly is a category of its own with its individual characteristics and styling challenges. Type 3a hair features loose ‘S’ shape curls that appear flatter than its other type 3 subtypes. Similarly to the type 2c hair, type 3a is difficult to style and straighten with distinct frizz and a coarse texture. Type 3b hair is dense and coarse in structure with tight ‘S’ shape curls or corkscrew curls that appear more voluminous than type 3a hair.

Type 3c hair has a distinct corkscrew with a circumference of either a straw or a pencil, or a thin marker. This curly hair subtype is prone to dryness and damage; oil from the root is unable to efficiently reach the tip of the hair shaft as a result of the obstruction created by the ringlet curl.

Coily Hair Type

Coily hair has densely packed wiry coils. Type 4 often needs much more moisture and is a bit more fragile and prone to breakage. The most common complaint is styling. Type 4 hair is often undefined and relies on dense products to improve coil definition. Type 4a hair has wiry, ‘S’ shaped coils with minimum shrinkage. This coily hair subtype has dense springy coils that can comfortably surround a crochet or knitting needle.

Type 4b has a ‘Z’ shaped coil that bends sharply into various angles with up to 70% shrinkage from wet to dry hair. When it comes to definition, type 4b has less definition than type 4a hair without specialized products and has the circumference of a pen or pencil. Type 4c has a tight, undefined coil with a scalp zigzag pattern and the highest shrinkage from wet to dry.

Why does the hair type chart matter?

After going through the hair test, you may find that your hair is a mix of different types-curly but highly porous, or fine but extremely dry. Either way, having a thorough evaluation and understanding of your hair type will make it better and easier for hair care decisions and help ensure that your strands always look and feel their best.

Is there a difference between Male and Female hair?

There are not any great biological differences between male and female hair. However, there are other aspects that may differ between the genders such as hair loss (which is genetic) and differences in hair thickness and texture when it comes to body hair, which is influenced by hormones.

The pH of Hair and Scalp

The last major important property of hair, not related to the particular hair type, but extremely important nonetheless is pH. Hair is very sensitive to changes in pH. Hair is acidic and is naturally negatively charged, so anything alkaline can create friction. This can lead to damage and breakage.

Since water is neutral at around pH 7, which is more alkaline than the hair. Which is acidic at 3.67. It can actually increase friction between hair strands, cause frizz and make wet hair difficult to comb. But there’s more: at alkaline pH levels, hair has an increased ability to absorb water and swell, lifting the cuticle cells. Water can penetrate the lifted cuticle cells and temporarily break hydrogen bonds of the keratin molecules making the hair shaft more prone to damage. To smooth down the cuticle cells and prevent damage, we need to seal the cuticle.

Cuticle cells lie flat and smooth on the hair strand when they are healthy but can be disturbed by various factors such as the ones mentioned: high pH, too much water or heat, friction etc., which causes them to lift giving the effect of frizzy, unsmooth hair. To smooth the cuticle cells down to a flat position, acidic products in the correct pH need to be used. Often an acidic hair rinse, or ACV rinse is recommended for smooth, shiny and more manageable hair.

Scalp pH is the same as the skin, at around 4.5 to 5.5, however the hair shaft is even more acidic at about 3.67. Shampoos don't have a standardized pH, the way skin products do,however salon products do tend to have a lower pH, because this is simply better for the hair. No tears shampoos have a pH of around 7, which is neutral, so as not to sting my eyes.

This means though, that the shampoo is more basic than the hair shaft and can therefore actually lead to damage. Always keep porosity and pH in mind when it comes to hair care products.

Final Thoughts

In conclusion, educating ourselves about the inner workings of our hair is an essential component that we all require in order to design and construct a hair care regimen that is tailored to our own hair type, allowing us to have lustrous and thriving locks as our crown.

References:

ZENANI

The Anatomy of Hair: everything you need to know about hair.

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