[Hair structure]

Hair is roughly divided into three layers. The outermost tissue is called the cuticle, the middle part is called the cortex, and the center part is called the medulla.

【cuticle】
The thin, translucent protective film on the surface of your hair is made up of 4 to 10 overlapping layers, forming a scale-like structure. The cuticle functions to protect the inner tissues of the hair, and because it softens when wet, it can be rubbed by brushing, etc., or chipped or peeled off when it dries. Also, the number of cuticles decreases towards the ends of the hair.

[Cortex]
Cortex is a tissue that makes up 90% of the hair, and it retains moisture, which affects the strength, elasticity, color, transparency, and luster of the hair. The protein/lipid structure and water content in this area affect the flexibility and thickness of the hair. Also, melanin pigment is mainly contained in this area, and the type and amount of melanin determines the color of the hair.

[Medulla]
This is a tissue located in the center of the hair, and is present in thick hair but often absent in thin hair.

The cortex is made up of fibrous bundles and surrounding structures, and if you look closely, they are made up of bundles of spiral keratin. Keratin is the main component of hair, and side chain bonds (disulfide bonds, ionic bonds, and hydrogen bonds) connect adjacent keratin fibers. Side chain bonds are easily broken by external stimuli, resulting in split ends that split vertically.

[Causes of hair damage]

It turns out that damage to the hair cuticle and cortex causes hair damage.
The cuticle and cortex degenerate, resulting in dry, split ends, and breakage. Also, the side chain bonds that hold keratin together are easily broken, so avoid split ends vertically.

Possible causes of hair damage include:
・Chemical effects such as color and perm
・Mechanical effects such as brushing
・Physicochemical effects such as ultraviolet rays and heat from hair dryers

It is important to take care of your hair while paying attention to the wear and tear, heat, and chemical effects that occur on a daily basis.

As you age, you may notice a change in your hair that has lost its shine, but this is likely due to the frizz of your hair. As we age, the appearance of frizzy hair increases (Figure 3-1), and the luster decreases (Figure 3-2).

The beauty of hair reflects the properties of the part called the "hair shaft" that is exposed on the surface of the skin. However, the hair shaft is already a collection of dead cells and cannot repair itself once it is damaged. This leads to hair breakage, split ends, and frizz.
Hair roots, on the other hand, are located inside the skin and are not harmed by the outside world. The hair shaft is in a healthy state as soon as it emerges from the skin's surface. How you maintain this condition will determine the beauty of your hair.