KEMA Column ｜ Hair Knowledge

Everything About Hair — A Complete Guide to Structure, Damage, and Care

Advanced · Quality · Oriented

We wash, dry, and tie it every day—yet, despite being so familiar, if asked, "What is hair made of in the first place?" or "Why does it get damaged?" most of us struggle to provide a good answer. This article is a "complete guide" that walks you through everything from the mechanics of hair to the causes of damage and daily care. By the time you finish reading, you will understand the clear purpose behind every step of your routine.

PART 1 ── What is Hair?

Actually, hair is "no longer alive"

It may come as a surprise, but the hair we touch is not composed of living cells. The only part that is alive is the "hair root" inside the scalp. New cells are created here, and as they are pushed upward and harden, they become the hair we see. In other words, just like the surface of your nails, the visible part of your hair is "fully grown" tissue.

That is precisely why hair cannot heal itself. While skin can regenerate over time, damaged hair cannot return to its original state. This is the fundamental premise of hair care. It is not about "healing," but rather preventing further damage and protecting and conditioning the current state—this is the true role of hair care. Keeping this in mind, let’s take a look at the structure of hair.

Hair has a "three-layer structure"

If you zoom in on a single strand of hair, you can see a three-layer structure, much like a pencil. The outermost layer of scale-like film is the cuticle, the thick layer inside is the cortex, and the core is the medulla. Each has a role, and your hair's shine, manageability, and texture are determined by the condition of these three layers.

Cuticle = The "scales" that protect hair

The outermost cuticle covers the surface of the hair, overlapping like roof tiles. Its role is to act as a "barrier" that traps internal moisture and nutrients while preventing external damage. When these scales are closed and aligned properly, they reflect light smoothly, creating that characteristic "shine." Conversely, when the scales lift and open, light reflects irregularly, making the hair look frizzy and allowing its contents to escape.

The cuticle is most vulnerable when the hair is wet. When it absorbs water, the scales open, making them very susceptible to friction. This is why wet hair is easily damaged by vigorous towel drying or sleeping while damp. There is a very real reason behind the basic rule of "treating wet hair gently."

Cortex = The "substance" and personality of hair

Inside the scales, the cortex makes up about 80–90% of the hair. It consists of protein (keratin) fibers and moisture, and this layer determines the hair's body, firmness, elasticity, waviness, and even hair color. Most of what makes a person's hair "theirs" resides in the cortex. When this layer is damaged by color treatments, perms, or intense heat, the hair loses its body and becomes frizzy and unmanageable. This is why care that replenishes the inside, rather than just treating the surface, is essential.

The often-overlooked protagonist: The "field" known as the scalp

While we often focus on the hair itself, it is the scalp that produces it. The scalp is like a "field" for your hair. Just as a good crop cannot grow in poor soil, an imbalanced scalp environment will compromise the vitality of hair yet to grow. Healthy hair can only be born from a healthy scalp.

Since the scalp is part of the skin, it is affected by sweat, sebum, dryness, and UV rays. If pores become clogged with sebum or if the scalp becomes dry and stiff, the foundation for hair growth wavers. This is why Korean hair care emphasizes "soil preparation," using not just shampoo but also scalp tonics and serums. Even gently massaging it with the pads of your fingers is a wonderful way to care for your scalp.

PART 2 ── Why Does Hair Get Damaged?

What actually happens when hair is "damaged"?

Once you understand the structure of hair, the true nature of "damage" becomes clear. Simply put, hair damage is a state where "the structure of the hair is disrupted and internal components are lost." Healthy hair has a closed cuticle that protects the inside, with a cortex that firmly holds onto protein and moisture. Damage means this balance has collapsed. The cuticle peels open, moisture, protein, and lipids leak out, and the interior thins and becomes hollow—damage is not just a "surface problem," but a chain reaction where the rupture of the surface defense leads to internal depletion. So, where do the "factors" for this come from? There are four main ones.

Factor 1
The "physical" force of friction

The most easily overlooked factor is daily friction. Brushing, towel-drying, rubbing against a pillow, hair tangling—these are all small forces, but repeated daily, they gradually wear away the tips of the cuticle. Wet hair is especially defenseless. When drying with a towel, "press, don't rub," and when brushing, use a wide-tooth comb to detangle starting from the ends. Using leave-in care to create a protective film on the surface can significantly reduce friction.

Factor 2
Heat changes protein

While heat from blow-dryers and flat irons is a great ally for styling, it can be a major cause of damage if handled incorrectly. Protein, the main component of hair, undergoes "thermal denaturation" when exposed to high heat, changing its properties. Much like an egg white that hardens when heated and cannot return to its original state, denatured protein cannot be repaired. Excessive heat creates hollow cavities inside the hair, robbing it of its elasticity and moisture.

Here, I want you to understand the concept of "damp heat" that KEMA has long cherished. A straight iron is the most obvious example. Irons use "heat" to style hair, but applying high heat to bone-dry hair will strip away any remaining moisture and damage the cuticle. Conversely, if you apply the right amount of heat to hair that contains the appropriate amount of moisture, the hair will smooth out and become shiny. In other words, what makes hair beautiful is not the heat itself, but the balance between moisture and heat. Before using an iron, replenish moisture with leave-in care, don't set the temperature too high, and don't hold it in one spot for too long—these are the tricks to making heat your "ally" rather than your "enemy."

Factor 3
The "chemical" force of color and perms

Hair color, bleach, and perms are treatments that use chemicals to act on the inside of the hair to change its color or shape. While they provide beautiful results, they are the most significant factors for damage because they involve altering the structure itself. Bleaching breaks down pigments while loosening protein bonds, and perms break and reform the bonds that maintain the hair's shape. In either case, hair is left in a delicate state afterward.

The important thing is not to avoid these treatments, but to design a care routine for afterward. Chemically treated hair tends to lack internal protein and moisture. It is essential to adopt a mindset of replenishing the inside, not just fixing the surface. KEMA’s advanced liposome technology is designed to deliver repair ingredients deep into the hair. The more you enjoy colors and perms, the more your daily care—premised on internal repair—will help maintain your hair's beauty.

Factor 4
The "environmental" force of UV rays, dryness, and oxidation

The environment we are exposed to every day is surprisingly neglected. Many people apply sunscreen to their skin but leave their hair and scalp unprotected. UV rays damage the protein, lipids, and pigment on the hair's surface, leading to dryness and fading. Dry air robs hair of moisture, and the oxidation of sweat and sebum causes odors and stiffness. On days you spend outdoors, protect yourself physically with a hat and use leave-in care to create a moisturizing film before you go out. At the end of the day, reset oxidized sweat and sebum immediately. "Prevention" is the shortest path to dealing with environmental damage.

How damage progresses — 4 stages of cuticle degradation

Damage caused by these four factors doesn't instantly turn into split ends. In many cases, the state of the cuticle changes in stages. The diagram below illustrates this progression.

During stages 1–2, it is easy to maintain shine with leave-in care and friction countermeasures. However, by stages 3–4, the cortex is exposed through the worn-down cuticle, manifesting as tangles, breakage, and split ends. Unfortunately, once hair tips have reached this point, they cannot return to their original structure. That is why it is important to notice the signs early and prevent further progression.

"Wet-dry" fatigue you should know about

There is another commonly overlooked phenomenon. Hair absorbs water and swells when wet, and shrinks when it dries—this constant daily cycle of swelling and contraction gradually tires out the hair, much like how a rubber band loses its integrity from being stretched and released. This is also known as "hygral fatigue."

Hair is reborn. But damage "cannot be cured."

Here is a little reassuring news: Hair goes through a cycle ("growth -> extension -> shedding -> regrowth") at its own pace. It is a natural part of this renewal for dozens of hairs to fall out daily. You don't need to worry about all hair loss.

On the other hand, hair that has already grown out does not have the power to heal itself. Therefore, there are two main goals for care: "prevention" to stop further damage, and "repair" to replenish lost components and condition the opened cuticle to restore its appearance and texture. Prepare your scalp for the hair that will grow in next, and gently protect the hair you have now. These two approaches together help grow beautiful hair.

PART 3 ── How to Care for It

The KEMA approach to hair — Protect, Replenish, Condition

Knowing the mechanics behind your hair makes what you need to do very simple: Protect—reduce friction and shield hair from heat and UV rays. Replenish—repair components lost to color treatments and heat from the inside. Condition—be mindful of the moisture and heat balance (damp heat) to achieve a shiny finish. These three pillars represent the philosophy of order, balance, and harmony that KEMA stands for.

Specifically, treat wet hair gently after washing, create a moisturizing film with leave-in care, and dry it quickly at a temperature that isn't too hot. On days you use an iron, always be mindful of the balance between moisture and heat. Treat the scalp as a "field" daily, and make it a habit to use oils or balms that focus on internal repair for the ends. There is nothing difficult about it. The accumulation of small choices made with an understanding of how hair works will certainly change your hair a year from now. Daily care, armed with the knowledge of how your hair works, will surely become just a little more careful and cherished.

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