Hair Anatomy 101: The Foundations of Human Hair

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Have you ever had one of those days? You find yourself standing in front of the mirror, staring at the marvel that is your hair, asking yourself, “Why?” Why does my hair grow like that? Why are my curls so random? How did I ever end up with this color? Do your questions have questions?

Hair Structure - medulla, cortex, cuticle, hair shaft, sheath, matrix, hair bulb, sebaceous gland

Knowing our hair, the specifics of what we are actually dealing with and how it functions in the grand scheme of things, can make all the difference in the world when trying to achieve the latest look.

We regularly wage war with the tip and shaft of the hair strand, while the root and bulb do their thing below the surface. Starting from top to bottom, we’ll take a closer look at the anatomy of human hair and how its parts function together to create a healthy head of hair.

The hair shaft defines you

First and foremost, all hair, from root to tip, is made up of a water insoluble protein known as Keratin, which consists of many amino acids as its primary units.

Home of the split end, the tip of the hair is the part that we regularly trim off in order to keep the rest of the shaft healthy. It is possible for the split end to travel along the shaft and effectively sub-divide the natural thickness of your hair. When that happens, your hair will become weaker and more susceptible to breakage. Regularly trimming is recommended by hair professionals everywhere.

Within the shaft of your hair strand are the three main components, or building blocks, of human hair; the cuticle, cortex and medulla. It’s the internal chemistry and makeup of these which define the characteristics and manageability of your hair, in general.

You could say, the hair shaft holds the key to combating whatever hair insanity you regularly deal with. Excited to slay that dragon, we’re going to examine these building blocks now.

The building blocks of human hair

Cross section of hair - medulla, cortex, cuticle

There are three main components to the human hair shaft. Each of these are further subdivided and have their own complexities and challenges. Starting from the outside in, the shaft is comprised of:

  • a cuticle
  • cortex, and
  • medulla.

What’s so cute about the cuticle?

The cuticle layer is clear and absent of any hair color or pigmentation. It is the reflective element light bounces off of to radiate shine. The tighter closed or more smooth the cuticle layer is the more shine your hair will display.

Every cuticle is formed out of a series of layers of dead cells. If you think about the shingles on the roof of a house, you can easily visualize how the cuticle layers might overlap on an individual hair strand.

It is important to note, not every hair cuticle is created equal. There can be variations in thickness from as little as 2 layers up to 10. Surprisingly, these variations can occur on a single strand of hair, as well as between different hair strands on the same head of hair.

The gatekeeper and first line of defense.

As a protective layer, the cuticle acts as a gatekeeper and strives to keep unwanted elements external to the hair shaft, while keeping beneficial elements, like moisture, inside.

Because of the multiple layers, there is a substance between each which binds them together so that they operate as one unit. The damage of that substance through chemical treatments, styling products and styling practices causes the layers to separate and reduce the overall protective quality.

As the first line of defense for your cortex and an important element in the finishing of your crowning glory, you can see why it’s important to keep the cuticle healthy and at its best.

Let’s see how the cortex works alongside the cuticle.

Sometimes the core. Always the cortex.

Because the medulla is not present in all hair types, the cortex can sometimes act as the core or centremost part of certain hair shafts. Whether the medulla exists or not, the basic structure of the cortex remains the same.

Much like the cuticle, there are multiple cells that work together to form the cortex. The cortex is the thickest part of the hair when considering the diameter of a single hair strand. It is made up of a series of protein-based rod-shaped cells that run parallel to the length of your hair. These cells are not always a uniform shape. TODO The cortex: Giving substance to the human hair shaft  – explores these differences and more in greater detail.

Defining your hair color.

Within the cortex, you’ll find the major source of your hair color. Your individual pigmentation or melanin content resides here and dictates the hue of your tresses.

It is the cortex, where keratin protein accumulates, that needs to be accessed in order to change hair color  with dyes and chemicals. The keratin cellular chemistry is what is changed to create new colors and styles.

When the medulla layer is actually present, there can be some melanin cells found there as well. Read on for more information on this “now-you-see-it-now-you-don’t” layer.

Maybe the medulla. Maybe not.

The medulla, found at the core of some hair strands, appears to be the greatest mystery to hair care specialists and scientists today. As you search the internet, you’ll discover the definitive conclusion that the medulla layer is not present in fine hair, whatever the color.

The underlying function of the medulla is still in question. Dr. Ali N. Syed, chemist and founder of Avlon Industries Inc. with over 30 years experience developing hair care products, states that the medulla is full of air pockets and suggests it may be responsible for any potential volume found in particular hair types.

It’s the criminal forensic scientists that get the credit for documenting different types of medulla. They have discovered a variety in the structure of the medulla across different hair types and have created four categories for medulla classification:

  • continuous
  • interrupted
  • fragmented, and
  • absent.

They also claim that Native American and Asian hair types have been found to have continuous medulla as well as coarse hair, since instances of double medulla has been found in men’s beard hair.

Medulla may not be so mysterious.

Black Hair Spot would like to be the first to draw some conclusions from the data they have gathered. First, take into account Asian hair and Native American hair tends to be bone straight and highly resistant to chemical restructuring, in the case of perms and waves. Then add to that the fact that beard hair, where double medulla had been identified, is typically classified as very coarse. We can deduce that the medulla layer plays a strong role in the pliability of the hair shaft and overall structure in hair typing.

A good metaphor for comparison might be a spinal column, since a medulla runs through the centre of your hair shaft, when present at all:

  • continuous or unsegmented would be likened to rebar, inflexible and straight.
  • interrupted and fragmented would show signs of variable flexibility dependent on the frequency and space between naturally occurring gaps.
  • complete absence of medulla would experience flat, lifeless hair that is difficult to hold shape or style; you might say, spineless.

With this assumption in place, it appears that the most extreme classifications of the medulla layer, continuous and absent, prove to be the most difficult to alter chemically.

We’re excited to see where the scientists, who are pursuing this subject, land. Whether or not the medulla is critical to the shape and style of your hair, one thing is for certain. Your hair would be nothing without the following supporting actors.

Introducing the supporting actors in your hair health story

It’s no secret that your hair health is contingent upon what nutrients you supply internally and what you expose it to externally. Those hair headliners of yours may claim the credit, but they don’t do it all by themselves. They have the benefit of some strong supporting actors, which help you to command the attention you deserve for those beautiful tresses. In truth, your hair wouldn’t even exist without these below the surface supporters.

In particular, your tresses are supported by:

  • the hair follicle,
  • hair bulb, and
  • sebaceous gland.

Time to take a closer look at how they help your hair to steal center stage.

The fortitude of the hair follicle.

The hair follicle is more in control than you might think. While we’re frantically trying to restyle the hair north of our scalp, the hair follicle is hard at work replicating that same genetic template we’re working overtime to defeat.

According to, the entire inventory of our hair follicles, their distribution and spacing across our entire body is formed in the earliest days of our womb experience. That means whatever you’ve got is what you’ve got, for the duration. Keeping them all functioning is your best hope for maintaining hair density. See Human hair follicle: Your hair growth factory for more information about the follicle and reasons why it may fail to produce hair.

One might assume all follicles look the same and differentiation in hair type only shows itself once it emerges from the scalp or skin. Not so.

Think of follicles like tiny hair factories with preset molds inside. As the hair grows, it travels through this genetically designed mold  and comes out the other side with your established  curl pattern. So if your hair has tight tiny curls, the embedded path reflects that. Large curls? Same thing, different path.

The follicle’s main job is to produce and “house” the hair. It has its own system for growth, shedding and regeneration, so it’s always on the job replicating your trademark tresses. The hair fibre is rooted inside the follicle until it is shed for new growth.

Hair bulb: the anchor of your hair strand

The hair bulb is located at the very bottom of the hair follicle and is the anchor that roots the hair into the skin. It contains the living cells, which divide and replicate, and reproduce the hair strand.

According to, blood vessels nourish the cells in the hair bulb and deliver the hormones responsible for common modifications of hair that occur at different stages of your natural life. Graying hair or change of texture and density are common as we age.

It is the hair bulb that has a mass of nerve endings. These are the source of the pain you feel when someone pulls your hair. They do not travel along the length of the hair shaft, which is why you don’t feel pain when your hair is cut. That part of your hair is actually dead.

Those nerve endings are also responsible for the goose bump feeling you get or even the ability to notice when someone has brushed up against your locks when you aren’t looking.

Sebaceous glands: our built-in oil refinery.

Responsible for keeping your skin and hair moist, the sebaceous gland is a sac that is located in the skin. It produces an oil called sebum, which empties into the duct of the follicle. This provides lubrication and moisture as the hair shaft grows up to maturity.

Not all sebaceous glands produce oil at the same rate. Another dictate of genetics, a person can expect anywhere from dry, moderate, oily and very oily effects from this gland’s output. See TODO The sebaceous gland: Oil shortage or overdrive for more information.

Also not uncommon are variations in the amount of secretion throughout the anatomy of any one person. If you’ve ever experienced dry scalp but have an oily T-zone on your face, you’ll understand completely.

Sometimes your hair follicle can be blocked with dead skin cells. When that occurs, the sebaceous gland doesn’t know to stop production so sebum fills up the duct and a plug forms. If you’ve ever had hair bumps, or acne, this is an example of your blocked follicles at work.

On the plus side, sebum is responsible for protecting the body from bacteria, while keeping moisture locked in.  When it finds its way to the scalp, or epidermis, it begins to perform this protective role. Vitamin A is reported to be beneficial with sebum production and may be important if you’re trying to have a more supportive relationship with your sebaceous glands.

There is much more to our hair than meets the eye. This broad overview is intended to start the journey, unwrapping the mysteries that both confuse and astound us, as we go.

This exploration is far from over. Check back with us as we continue to share more educational content in this series.

If you happened to learn something that you didn’t already know, please leave a comment sharing how we blew your mind today. Even if your mind wasn’t blown, if you were alerted to something new, we’d love to hear from you.

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