What is hair made of?

The hair shaft has three layers: the cuticle — protective scales on the outside; the cortex — keratin fibers and pigment, making up the bulk of the shaft; and the medulla — a soft core that is not present in all hair types. The shaft itself is not alive; the root sits in a follicle in the scalp — that is where hair grows. Understanding this structure makes it easier to evaluate hair care products: some work on the cuticle, others penetrate the cortex. This also helps to be skeptical of claims that products can 'revive' already-grown hair.

Why is hair made of keratin?

Hair is approximately 90% keratin — a strong structural protein responsible for its strength. The rest consists of water, lipids, pigment, and trace elements. This is why the logic of proper hair care is straightforward: proteins replenish the protein framework, while oils and humectants provide smoothness and moisture retention. The balance of protein and moisture is what makes hair simultaneously strong and elastic. A shift in either direction results in hair that is either brittle or limp and mushy.

Can damaged hair be restored?

Not fully. Grown hair is a non-living structure — it cannot be 'healed' the way skin can, and no new cells form within it. What hair care can do is fill in damage, smooth the cuticle, and strengthen the shaft so that hair looks and behaves better. However, a damaged section does not regenerate, which is why prevention is always more important than restoration. Protecting hair from unnecessary damage is far more effective than trying to rescue it afterward.

Why does hair lose its shine?

Shine comes from a smooth, tightly closed cuticle that reflects light evenly, like a mirror. When damaged — by lightening, heat styling, or hard water — the cuticle scales lift, the surface becomes rough, and light scatters instead of reflecting. This is why dull hair tends to also frizz, tangle, and struggle to retain moisture. Restoring shine requires care that smooths the cuticle and protection from further damage.

Hair Structure: Cuticle, Cortex, and Why Hair Gets Damaged

Hair structure: the shaft consists of three layers — the cuticle (overlapping outer scales that govern shine and protection), the cortex (keratin fibers and the pigment melanin — responsible for strength and color), and the medulla (a soft inner core, absent in many hair types). Nearly 90% of the hair shaft is made up of the protein keratin; the rest is water, lipids, and pigment.

"Hair is just hair — how complicated can it be?" And then you're standing in front of a shelf, not knowing what to pick: one shampoo promises "structural restoration," another "keratin sealing," a third "nourishment from within." To stop buying promises and start buying results, all it takes is understanding how a strand of hair is actually built. That knowledge makes your haircare routine click into place: you can see what a shampoo genuinely does, what proteins repair, what oils do, and what's simply well-written marketing. Let's break it down in plain terms — no jargon.

Quick summary if you're short on time

Hair has three layers: the cuticle (a protective "tile" on the outside), the cortex (strength and color on the inside), and sometimes the medulla (a soft core that barely affects anything).
Nearly the entire hair shaft is keratin, a tough structural protein. That's why effective haircare revolves around three things: protein, moisture, and lipids.
Shine is about a smooth, flat cuticle; strength is about an intact cortex. These are different goals that require different products.
Damage always comes down to the same story: lifted scales and leached protein. That's where dryness, frizz, breakage, and dullness come from.
The honest truth: a grown hair shaft is a non-living structure. Haircare fills in and smooths over damage — it doesn't "revive" the hair. That's why prevention is always more valuable than damage control.

Now let's go deeper — it really won't take long.

Hair grows in the skin, but lives on the outside

First, two very different worlds. There's the hair root — it sits inside the scalp, in a tiny pocket called a follicle. That's where the hair is born, nourished through the bloodstream, and coated with sebum (the scalp's natural oil) that lubricates and protects the length. The root is alive.

Then there's the shaft — everything we see, brush, wash, and color. And here's the key point that changes the way you think about haircare: the shaft is already a non-living structure, much like a fingernail. Blood doesn't reach it; it can't heal the way a wound does. Everything we do externally is maintenance on a finished material. That sounds a little sobering, but it's actually liberating: it becomes clear what you can honestly expect from a product — and what you can't.

The three layers of the hair shaft

The shaft isn't a uniform thread — it's a layered construction with three distinct parts:

Cuticle — the outermost protective layer, made of flat scales overlapping like roof tiles. When the hair is healthy, the scales lie flat, the surface is smooth, and it reflects light evenly — that's where shine comes from. The cuticle takes the first hit from everything: brushing, heat styling, color, hard water.
Cortex — the main body of the hair, everything beneath the cuticle. This is where strength and elasticity live (in the keratin fiber bundles), and where color is stored — the pigment melanin. When people say "the hair structure is damaged" or "the hair has lost its elasticity," they almost always mean the cortex.
Medulla — a soft core at the very center. It's absent in many hairs (fine hair often has none at all) and has little effect on hair properties. You can safely forget about it — it barely responds to any kind of care.

If you take away just one thing: the cuticle governs shine and smoothness on the outside; the cortex governs strength on the inside. These are two different floors, and they're cared for differently.

What hair is made of

Now for the composition — and this explains the entire logic of haircare. Hair is nearly 90% keratin, a tough structural protein. The rest is water, lipids (fats), pigment, and a small amount of trace minerals. That's essentially the whole "recipe" of a hair strand.

Once this clicks, the haircare aisle stops being overwhelming. Every well-formulated product works on one of three things:

Protein (proteins and amino acids). They replenish the keratin framework of the cortex — this is about strength and resilience. Hydrolyzed proteins are small enough to penetrate the shaft and patch up weakened areas from within.
Lipids and oils. They seal the cuticle and coat the surface of the scales — this is about smoothness, shine, and protection. We have a separate, honest breakdown of oils.
Moisture (humectants — glycerin, aloe). They attract and retain water — this is about elasticity and a "alive," non-straw-like appearance.

A lopsided approach causes problems in any direction. Protein alone without moisture makes the hair stiff and brittle. Moisture alone without protein leaves it soft but limp and weak. Good haircare keeps all three in balance.

Why hair gets damaged

Nearly every type of damage is a story about the cuticle and cortex, and it follows the same pattern: the scales suffer first, then what they were protecting gets washed away.

Bleaching and ammonia-based dyes lift and literally break down the scales to reach the pigment — and strip protein from the cortex in the process. The most aggressive item on this list by far.
Heat styling without heat protection evaporates moisture and scorches the cuticle. Once or twice — manageable. Every day — it builds up.
Hard water, sun exposure, pool chlorine, and ordinary friction (a rough towel, a pillowcase, tight elastics) roughen the scales gradually and almost imperceptibly.

What follows is a chain of effects you'll easily recognize. The scales lift → the surface turns rough → the hair catches and tangles, loses shine (light no longer reflects evenly), and loses moisture through the damaged surface. The result: porous, dry hair that frizzes and breaks. All of these "symptoms" point to the same thing: an open, damaged cuticle.

And here's an important, unvarnished truth. The hair shaft that's already grown is not alive and cannot regenerate the way skin does. Haircare genuinely fills in damage, smooths the cuticle, and temporarily strengthens the shaft — the hair feels softer, smoother, and more resilient. But the damaged area doesn't actually "heal." That's why prevention is always a better investment than rescue: it's far easier to protect what's intact than to repair what's been destroyed.

How to read a label once you understand hair structure

The best part of knowing all this theory is that labels lose their power to manipulate you. Once you understand the three layers and the three building blocks, it's easy to separate substance from beautiful words:

"Restores structure," "nourishes from within" → look for proteins in the ingredient list (often listed as Hydrolyzed Keratin, Hydrolyzed Protein). This works on the cortex.
"Mirror shine," "smoothness," "frizz control" → these are lipids, oils, sometimes silicones. Cuticle-level work — superficial, but legitimate.
"Hydration," "elasticity" → humectants, glycerin and similar ingredients.
"Revives," "resurrects," "heals the hair" → nice words. Remember: the grown hair shaft isn't alive; there's nothing to heal, only to maintain.

Common haircare mistakes

Confusing shine with health. Silicones and oils deliver instant smoothness and shine, but that's surface-level care — not an internal repair. A shiny strand can still be porous and weak in the cortex. (Silicones without the myths — separate article.)
Overloading on proteins. "If protein strengthens hair, more must be better" — and the result is stiff, brittle, straw-like strands. Protein always needs a partner: moisture.
Heat styling without heat protection. That's a direct blow to the cuticle, every single day. Heat protection isn't a marketing gimmick — it's literally a barrier between your flat iron and your scales.
Expecting haircare to "fix" severely damaged lengths. It won't fix them — it will mask and temporarily reinforce them. Heavily damaged ends are honestly better trimmed off than endlessly nursed.
Ignoring the scalp. Hair is born in the follicle. Healthy lengths start with a calm, well-balanced scalp — which is why the foundation of any routine is gentle sulfate-free cleansing, not a harsh shampoo.

How to put this into practice

Now, the same logic translated into simple steps, layer by layer:

Protect the cuticle. Gentle sulfate-free cleansing, heat protection before blow-drying and straightening, careful detangling, and a soft towel. An intact cuticle is half the battle.
Rebuild the cortex with proteins. For strength and resilience — the Keratin line with hydrolyzed proteins that work directly on the keratin framework. We covered this topic in depth in our article on keratin restoration.
Don't neglect moisture and lipids. To keep hair elastic rather than dried out by protein — the Hydration line.
Read ingredient lists with intention. Understanding structure makes it easier to evaluate actives: for a breakdown of what we use in our formulas and why, see "The actives we use".

The entire professional Cosmex lineup is built on exactly this logic: a gentle base plus actives targeted at a specific layer of the hair — the cuticle or the cortex. We don't promise to "revive" a non-living structure; we care for it honestly. Made in-house in Almaty — see the full ingredient lists and pricing in the Professional catalog.