Hair is a very strange thing. It falls and sheds easily and all the time, but it’s also incredible strong. A single hair strand can support 100 grams (3.5 ounces) of weight, or 60 million times its weight. That makes anyone wonder: what is hair made of!?
To answer such an anatomical question, we must now explore the hair structure, what is hair, and how to take care this precious part of your body.
What is Hair?
The human body consists of approximately 5 million hair follicles, with just 125,000 located on the scalp. This shows how critical and important hair is: the only hairless areas of the whole human body are the palms, soles and lips.
But what is actually hair? What we call ‘hair’ is a structure made of 95% keratin which plays a crucial role in protection, thermoregulation and sensory perception. It has 2 main parts: the hair follicle, and the hair shaft.
1. What is a Hair Follicle? The Growth Center
The hair follicle is the part that lies underneath the skin (dermis). It is also called the ‘hair bulb’. It is hidden, invisible, and the primary structure where hair grows from, regulating the hair growth cycle (anagen, catagen and telogenphases).
The hair follicle consists of the inner and outer layer (ORS & IRS):
Outer Root Sheath (ORS)
The outer root sheath (ORS) is a powerhouse of stem cells, capable of transforming into different cell types like melanocytes and keratinocytes. These stem cells gather in a bulge region, playing a key role in hair regeneration and pigmentation.
Inner Root Sheath (IRS)
The inner root sheath (IRS) is made up of the Henle layer, Huxley layer, and the cuticle layer, which helps secure the growing hair shaft within the follicle. This anchoring process is strengthened by IRS cells producing keratins and trichohyalin, essential for hair structure and stability.
2. What is the Hair Shaft? The Visible Part
The hair shaft is the part of the hair that you see—dead but incredibly strong. Made almost entirely of keratin, it’s what gives hair its texture, color, and resilience. Once hair leaves the follicle, it has no regenerative abilities, meaning damage is permanent. That’s why keeping it healthy is key!
The shaft is structured in three distinct layers, each playing a unique role in hair’s strength, shine, and durability.
Cuticle (Outer Layer): The Protective Shield
The cuticle is the outermost layer, a thin but tough covering made of overlapping scale-like cells. These scales lock moisture in, keeping hair smooth and protected from external aggressors like UV rays, pollution, and heat styling.
When the cuticle is intact, hair looks shiny and feels soft. When damaged? Hello, frizz and breakage!
Cortex (Middle Layer): Strength and Colour
Beneath the cuticle lies the cortex, the thickest layer of the hair shaft. This is where keratin fibers and melanin pigments live, determining hair’s strength, elasticity, and natural color.
The cortex is why some hair is curly, wavy, or straight—it all depends on how the keratin bonds are arranged. Damage here leads to brittle, weak hair prone to snapping.
Medulla: The Mysterious Inner Core
The medulla is the innermost layer, but not everyone has one! It’s typically found in thicker, coarser hair and is thought to play a role in light reflection and structural support.
Fine hair often lacks a medulla entirely, and its exact function is still a bit of a mystery.
Hair Structure Diagram
Understanding hair helps explain why it behaves the way it does—why it sheds, why it breaks, and why it can be incredibly strong.
Below is a detailed hair structure diagram illustrating its different layers, from the follicle deep in the skin to the outermost cuticle of the shaft.
What is Hair Really Made Of? Its Chemical Components
Hair might seem simple, but at a molecular level, it’s a complex structure of proteins, lipids, and pigments that determine its strength, elasticity, and color.
Keratin: The Backbone of Hair
Hair is about 95% keratin, a strong fibrous protein that also makes up nails and the outer layer of skin. This protein is rich in cysteine, an amino acid that forms disulfide bonds, giving hair its toughness and shape. The more disulfide bonds, the curlier your hair!
Lipids: The Natural Hair Conditioner
Sebaceous glands release natural oils (lipids) that coat the hair shaft, keeping it soft, flexible, and resistant to breakage. But over-washing, harsh shampoos, and heat styling strip these oils away, leading to dry, brittle hair.
Melanin: The Pigment That Gives Hair Its Color
Melanin is responsible for your hair’s natural shade—eumelanin (brown/black) and pheomelanin (blonde/red). As we age, melanin production slows down, which is why hair turns gray or white over time.
Why Does Hair Break or Fall Out? (And What to Do About It)
Shedding is normal—but excessive hair loss or brittle, breaking hair can be a red flag. Let’s break down the biggest culprits on why hair can break or fall, before giving you a solution:
1. Heat & Chemical Damage
Blow-drying, straightening, bleaching—your hair remembers everything. High heat and harsh chemicals weaken the cuticle, leading to split ends and breakage.
2. Stress & Hormonal Imbalances
Ever noticed your hair falling out during stressful periods? Cortisol spikes (stress hormone) push more hairs into the telogen (resting) phase, causing noticeable shedding.
3. Poor Nutrition & Deficiencies
Your hair needs fuel to grow. Lacking certain vitamins, iron, biotin, or protein can make hair thin, weak, and prone to falling out.
4. Genetics & Medical Conditions
Sometimes, it’s not about what you do—it’s in your DNA. Conditions like androgenetic alopecia (one of the most common types of hair loss), DHT issues or thyroid disorders can lead to thinning and bald spots.
Concerned About Hair Loss?
Get a Free Consultation
If your hair is falling out more than usual, thinning, or breaking easily, it might be time to take action and consult a trichologst or dermatologist. Dr. Serkan Aygin Clinic specializes in hair restoration treatments, from PRP therapy to advanced hair transplants.
Book a free consultation today and get expert advice on the best solutions for your hair!
FAQs
What are the 3 main structures of the hair?
Hair consists of the cuticle (outer protective layer), cortex (middle layer with keratin and melanin), and medulla (inner core, present in thick hair but absent in fine hair).
What makes up 90% of hair?
Hair is 90-95% keratin, a strong fibrous protein that provides structure, strength, and flexibility. The remaining components include water, lipids, melanin (pigment), and trace elements.
Is hair dead skin cells?
No, hair is not made of dead skin cells. It consists of keratinized protein, which forms as living cells in the follicle die and harden, creating the hair shaft.
Does hair stop growing?
Yes, hair stops growing once it reaches the end of its anagen (growth) phase, which lasts 2-7 years. It then transitions into resting and shedding phases before a new hair replaces it.
What is the black thing at the end of a plucked hair?
The black or dark bulb at the end is the hair root, which was anchored in the follicle. It’s not the follicle itself but part of the hair strand’s base, sometimes surrounded by keratin and oil.
