The human hair is made of keratin, a helical protein that is also found in nails, skin, etc where some sort of physical protection is required. But to just say that hair is made of keratin and nothing at all would be incomplete. Human hair is a fascinating thing and it serves many functions, some that would fascinate you.
So to deeply look at the human hair, what is it made of, the anatomy, growth, and shedding of hair, we need more than “keratin” We look at what causes hair loss and it can be reversed. What causes hair to grow and are hair cells alive? Let’s start with the structure of the hair.
The human hair is made of a variant of keratin called alpha-keratin. This is the protein that makes hair, nails, claws, horns, etc. Alpha-keratin has a helical structure and it is produced abundantly in cells. After the protein is sufficiently made and infused, the cells die and the structure hardens. Hence you have hard nails and hair that can be cut without pain.
The reason alpha-keratin is used by the body to make hairs, nails, etc is because of its stability. Proteins are very prone to deformation due to heat, acidic, or basic environment or physical stress. Alpha-keratin is resistant to these stressors up to a certain degree. Notice how the hair shrivels when coming in contact with heat? That’s because heat changes the structure of alpha-keratin. But there’s more in hairs.
The anatomy of hair
To get rid of the confusion between the different parts of hair, let’s make a clear distinction. The part of the hair that you can see and touch is called the hair filament or hair shaft. We’ll refer to it as the hair shaft. The second part is the inner part that is deep set inside the skin (or scalp) which includes hair bulb, follicle, sebaceous gland, arrector pili muscle, etc. First, let’s see the hair shaft.
The layers of hairs
The shaft of the hair has three layers. Imagine a normal electric wire and its layers. The three layers are, starting from the outermost, cuticle, cortex, and medulla. All three layers have different functions and anatomy. We’ll touch over them briefly.
The cuticle: Have you ever seen a microscopic image of a human hair? Noticed that layer of scales overlapping the shaft like the covering of a corncob? This is the cuticle of the hair and it provides protection to the hair shaft and other layers of it, it also locks in the moisture and protects it from heat. Take a look at a microscopic image of the human hair shaft.
The cortex: This is the part of the hair which contains alpha-keratin, the protein that makes hair shaft. This is the bulk of the hair, containing keratin “rods” arranged like wires; in bundles. I have attached an illustration that gives you the general idea of how these layers are arranged.
The medulla: This is the central pith of the hair shaft, containing loose, unorganized, and soft material. The medulla is not found in all hairs, but it can be seen in scalp hair. Scientists are not very sure about all the functions of the medulla but it most probably is to add support to the shaft. It also contains the moisture that the cuticle protects.
Sebum: The natural conditioner
While the three layers mentioned above make the hair shaft, there is one more layer of wax and triglycerides released from the sebaceous gland. This layer covers the space between the cuticle scales. It gives hair a natural shine, helps keep the moisture in, and repels water.
As we age, men and women both lose the sebum that covers the hair, and hence, the hair becomes dry, weak, and loses its shine. Women lose sebum faster than men. This concludes the anatomy of the hair shaft. Now let’s dive deeper.
Hair roots: Follicle and hair bulb
The part of the hair that is inside the scalp or skin is called the hair root, placed inside the hair follicle. The hair follicle is a cup-shaped cavity that contains the hair bulb, the dermal papilla, and blood capillaries to provide nourishment for hair growth. Here’s a brief description of all.
Hair bulb: This part is called the hair root and contains living cells that create the hair shaft. These are actively dividing cells that produce keratin and other materials necessary for hair growth. The hair bulb sits at the base of the hair follicle and is connected to the dermal papilla.
Dermal Papilla: the dermal papilla is a bunch of cells that sit right below the hair bulb. What’s their job? They nourish and stimulate the cells in the hair bulb which helps in hair growth and keeping it healthy. So the dermal papilla is crucial for good and healthy hair. Do not be confused with dermal papilla and the white stuff that is at the end of a hair bulb. That is an unpigmented hair root.
Two peripheral organs are serving secondary functions. These two are; sebaceous glands and arrector pili muscles. Sebaceous glands, as established earlier, secret sebum which acts as conditioner and hair nourisher. Arrector pili muscles are not only found in the scalp but near all hair follicles. These muscles pull the hair shaft, erecting the hair when you get those goosebumps when you’re watching your favorite singer live or hear a sound at 1 am when you go downstairs to get something to eat.
How hair grows
The hair bulb contains living cells that produce keratin and other proteins that form the shaft of the hair. With the dead cells and accumulated keratin, the shaft is then pushed out and this is how hair grows. While the hair shaft is made of dead cells and keratin, there must be live and proliferating cells in the root for the hair to grow.
The dermal papilla is also crucial for hair growth along with blood capillaries and vessels. There are about 100,000 hair follicles in the human head. But then what’s hair thinning?
As established earlier, hair follicles are pockets in the scalp which contains hair root. But single follicles can contain multiple hair roots with multiple hair shafts. This is what gives your hair the dense appearance. But with aging and other factors, the number of hair shafts in one follicle reduce to one or two. This, along with the reduced girth in the hair shaft causes the thinning of hair.
Why do hairs turn white
What gives hair their natural color? Why do some people have black hair, some blonde, some red and white when they get older? This is because the color inside the hair dies. The human hair gets its color from the cells called melanocytes.
Melanocytes put the coloring pigment called melanin which gives hair its color. Too much melanin makes hair black, while none makes it white. The variation in the amount of melanin in the hair is the reason for different hair colors. So how why aging gives white color? Because melanocytes die and hence, there is no melanin produced.
Why is head hair different from pubic hair?
You must have noticed something. The hair on your head is thin, soft, fuzzy and easily managed. But the pubic hairs are opposite. They are short, coarse like thin wires. What makes the two different? The growth period makes these two different.
The hair on the head has a very long growth phase. They grow for 6-7 years and then shed after a few months. For the pubic hair, the growth phase is for mere months. This makes them short and crooked.
This marks the end of this article. Hope this article was elaborate enough to elucidate the subject of it. Here are some related articles that you may find useful;