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When it comes to caring for your hair properly, it helps to first understand what it’s actually made of. Hair might seem simple on the surface, but it has a complex and fascinating structure that plays a huge role in how it looks, feels, and behaves.
At its core, hair is made up of proteins called amino acids, held together by chemical bonds. These proteins form three distinct layers that each serve a unique function. Below, we’ll take a closer look at the different parts of your hair and explain what each one does.
The Hair Bulb
Each individual hair grows from its own hair follicle. The hair bulb is situated at the base of each hair follicle and contains your growing hair cells. These continually divide and push upwards, gradually hardening. Once they reach the upper part of the bulb, they arrange themselves into six concentric layers. The three inner layers become the hair, made up of the cuticle, cortex and the medulla (although the medulla isn’t always present, especially in hairs with a thinner diameter). The outer three layers become the lining of the follicle.
Specific cells in the hair bulb (known as melanocytes) make the pigment called melanin that gives your hair its colour. The shape of your hair follicle determines the shape of your hair (i.e. whether it is straight, wavy or curly).
Put simply, the bulb is where everything begins; from growth to colour to curl pattern. It sets the foundations for how your hair will look and behave once it emerges from the scalp.
The Hair Shaft
The hair shaft is the part of your hair which can be seen above your scalp. It is made of a protein called keratin (the same material nails, hoofs, feathers and claws are composed of) compacted and fused together.
Keratin is a remarkably strong protein and is very resistant to wear and tear. It is held together primarily by two kinds of bonds: disulphide bonds and hydrogen bonds. Disulphide bonds are extremely durable. In fact, they are one of the strongest naturally occurring bonds in the world. When you perm or relax your hair, these disulphide bonds are broken and reset into an alternative configuration. This is what allows you to permanently change the shape of your hair. Hydrogen bonds are weaker and more abundant than disulphide bonds. They help give your hair its flexibility. When you wet your hair, they are easily broken and can be temporarily reset with heat until they become wet again (either from water or humidity). This is what allows you to style your hair with hairdryers and tongs post-wash.
Essentially, the hair shaft is the visible part of your hair and the part you wash, style, colour and care for every day. Its unique structure explains why your strands can be both strong and flexible, yet also vulnerable to damage from heat, chemicals or environmental stress.
The Three Layers of The Hair Shaft?
The Cuticle
The cuticle is your hair’s protective layer, composed of overlapping cells. Think fish scales or roof tiles, but facing downwards. A healthy cuticle is smooth and flat. This gives your hair shine and protects the inner layers against damage. It also works to minimise the movement of moisture in and out of the underlying cortex, maintaining your hair’s hydration balance and flexibility. However, chemical processing and weathering can lift the cuticle and disrupt this balance, causing your hair to become dry and brittle.
The Cortex
The cortex forms the main bulk and pigment (colour) of your hair. It consists of long keratin filaments held together by disulphide and hydrogen bonds. The health of your cortex largely depends on the integrity of the cuticle protecting it.
The Medulla
The medulla is only present in thicker hair types. It is the innermost layer of your hair. It consists of a soft, thin core of transparent cells and air spaces.
Together, these three layers determine your hair’s strength, shine, colour and texture. Protecting the cuticle, in particular, is crucial for keeping your hair healthy overall.
Your hair’s structure might be complex, but understanding it is the first step towards treating it with the care it deserves. From the bulb that fuels growth to the protective cuticle that keeps your strands strong, each layer plays an important role. With this knowledge, you can make more informed choices about your haircare routine, helping you maintain healthier, stronger and shinier hair in the long run.
How Do You Treat Female Pattern Hair Loss?
Q: What is the primary function of hair in the human body?
A: Hair does more than just look good… it actually has several important jobs. It protects your scalp from sun, dust, and other environmental elements, and helps regulate temperature by keeping your head warm. Hair follicles are also very sensitive, so they contribute to your sense of touch.
Q: How does hair colour develop?
A: Hair colour comes from special cells in the hair bulb called melanocytes, which produce the pigment melanin. There are two main types of melanin: eumelanin, which creates brown and black shades, and pheomelanin, which produces red and yellow tones. The mix and amount of these pigments give each person their unique hair color… most of which comes down to genetics.
Q: How does the structure of hair vary among different hair types?
A: Hair structure isn’t the same for everyone. It depends on things like the shape of the hair follicle, the thickness of the strand and how the proteins inside the hair are arranged. For example, straight hair usually comes from round follicles, while curly or kinky hair grows from more oval or flattened follicles. Differences in the cuticle and keratin in the cortex also affect things like strength, elasticity and even shine.
Q: What can damage or change the structure of hair?
A: Your hair’s structure can be affected or altered by both external and internal factors. External factors include chemical treatments like colouring or relaxing, heat styling and environmental stress like sun, pollution, and humidity. Internal factors, such as genetics, diet, hormones and overall health, also play a big role. These influences can all weaken the hair, make it dry or brittle or lead to breakage and split ends.
Q: What factors affect the structure and health of hair?
A: Hair health also comes from a mix of internal and external influences. Genetics determine your hair type and thickness, while nutrition provides the building blocks for strong, healthy strands. Hormonal changes (like those during puberty, pregnancy or menopause) can also affect hair growth and texture. On the outside, environmental factors like sun exposure, humidity, and pollution can damage hair, and hair care habits (including heat styling and chemical treatments) can either protect or weaken it over time.
Q: What are the main differences between straight, wavy and curly hair?
A: Hair texture is shaped by follicle shape (the angle at which the hair grows) and the way keratin proteins are arranged in the strand.
Straight hair: from round follicles, lies flat and often looks shiny.
Wavy hair: from slightly oval follicles, creating gentle waves.
Curly hair: from oval or asymmetrical follicles, forming spirals or ringlets with more volume.
Kinky/coily hair: from very flattened follicles, creating tight coils and lots of texture.
These structural differences affect more than just appearance - they influence strength, elasticity, moisture retention and how easy it is to style.
