Just Like Skin, Hair Health Depends on Its Building Blocks

Although the skin and hair that we care for every day may appear to be completely different tissues, they are surprisingly similar in that they share basic structural components. In this content, we will take a closer look at the roles of the key components that make up hair, and what changes occur when these components are damaged.

｜1. Protein: The Framework Responsible for Hair Strength

Approximately 65–95% of hair is composed of protein, most of which is keratin. Keratin is also present in the stratum corneum of the skin, but in hair, it is significantly harder and stronger, playing a key role in maintaining the hair’s shape and elasticity.

Surrounding the keratin structure is another group of proteins known as keratin-associated proteins (KAP). These proteins sit around the rigid keratin fibers and help connect them, reinforcing the overall structure of the hair. In simple terms, if keratin forms the pillars of the hair’s framework, KAP helps hold those pillars together, enhancing structural stability. Thanks to this combination of keratin and KAP, hair is better able to withstand changes in the external environment.

Just as a decrease in collagen and elastin in the skin leads to visible loss of elasticity, similar changes occur in hair when these proteins are lost. The proteins that make up hair are strong but not permanent, and they can be broken down or severed by chemical treatments, heat, and UV rays. Over time, gaps form within the hair’s protein structure, causing the hair to feel rough and dry.

So, is simply supplying a large amount of protein the solution?

The answer is no. Rather than applying intact proteins directly to damaged hair, it is more effective to deliver ingredients in forms and sizes that the hair can actually absorb, such as peptides and amino acids. Peptides, in particular, are short chains of amino acids that are small enough to fill damaged areas while still carrying the information needed to help restore a strong hair structure.

｜2. Moisture: A Key Factor That Keeps Hair Flexible

Hair typically contains about 10–15% moisture. When moisture is well balanced, hair feels soft and flexible. However, hair is highly sensitive to changes in surrounding humidity. Excess moisture can cause the cuticle to lift, while insufficient moisture leaves hair dry, stiff, and more prone to breakage. For this reason, maintaining moisture balance—just as in skincare—is essential. At the center of this balance lies one critical component: lipids.

｜3. Lipids: The Hidden Key to Hair Health

Lipids account for approximately 1–8% of hair. Lipids are synthesized together within the hair follicle and move upward along with the hair shaft, or they may be replenished as sebum from the scalp travels down the hair. Although their overall proportion is relatively small, they exist both inside and outside the hair and perform a wide range of important functions.

• Reduction of surface friction: The outermost layer of the hair shaft, the cuticle surface, is bonded to an invisible lipid layer called the F-layer (18-MEA). It keeps the hair surface smooth and prevents friction or tangling.
• Barrier function: Lipids act as protective barriers both on the surface and inside the hair. Surface lipids help prevent excessive moisture loss. Inside the hair, a lamellar lipid structure composed of ceramides, fatty acids, and cholesterol functions much like the skin barrier, limiting excessive moisture penetration and blocking external irritants.
• Moisture transport pathway: Lipids inside the hair prevent external substances from entering indiscriminately, but they do not block them completely. Between the precisely arranged lipids, there are microscopic pathways through which moisture can pass. This is why hair gradually becomes wet during shampooing. Thanks to this lipid function, hair is protected from damage caused by sudden swelling and can maintain a stable overall moisture balance.
• Structural adhesion of hair: Lipids are present between cuticle layers, at the boundary between the cuticle and cortex, and throughout the cortex itself, holding each layer in place. Acting as a natural adhesive, they help hold each layer of the hair in place, allowing the structure to remain intact.

When lipids are depleted, this internal adhesive force weakens. Cuticles lift more easily, moisture escapes too quickly—or enters too readily—and damage accelerates. In this sense, lipids are a key component that protects both the structural stability of hair and its moisture balance at the same time.

｜4. Melanin: Determination of Color and Protective Function

Melanin, which accounts for approximately 3% of hair, is produced together when hair is formed in the scalp and is naturally located inside the hair (hair cortex). Since it exists in the hair cortex, which makes up the largest portion of the hair, it is a key factor that determines hair color. Just like our skin, the ratio of two different types of melanin — eumelanin and pheomelanin — creates a wide range of natural hair colors. Beyond color, melanin also plays a protective role by helping shield hair from UV-induced damage.

｜5. Minerals and Vitamins: Trace Components

According to research findings, small amounts of vitamins and minerals are present in hair. Although hair itself is a dead tissue, its formation process is influenced by the internal environment of the body, which means the levels of these trace components can vary. For this reason, nutritional status can be assessed through hair analysis.

｜Hair Components and Hair Care

In this way, the components that make up hair maintain a healthy hair condition by forming a balance through their respective roles. However, due to aging, heat, chemical treatments, and shampooing, these components are gradually lost. In particular, the older the hair is, and the farther it is from the scalp, the more easily its components are depleted, leading to damage. This process is similar to skin aging, in which the loss of ceramides, collagen, and moisture results in visible signs of aging. Effective hair care must therefore focus on filling gaps both inside and on the surface of damaged hair. In other words, truly restorative solutions support hair by replenishing protein-derived peptides and amino acids, natural lipids, and moisture-retaining ingredients.