What do the three layers and four keys of hair do?

Hair can be divided into three parts from the outside to the inside: epidermis, cortex and medulla. Hair epidermis is a fish-scale thin sheet formed by overlapping flat cells, which is arranged from hair root to hair tip and wraps the inner cortex. Although this protective film is very thin, accounting for only 65,438+00%-65,438+05% of the whole hair, its performance is very important. It can protect the hair from the external environment and keep it. It has a certain hardness but is fragile and has poor friction resistance. Too much bad shampoo is easy to hurt and fall off, and the hair is dry and dull. The hair cortex is located on the inner side of the hair epidermis and consists of tiny fiber cells containing many melanin. The main component of fiber cells is keratin, which is composed of amino acids. Many spiral fibrils make up small fibers, and then many spiral small fibers make up large fibers. Then several large spiral fibers form the outer fiber, which is the main part of the hair cortex. Hair cortex is the main part of hair, accounting for almost 85%-90% of hair. Melanin contained in cells is the key to determine the color of hair. China's head is black because there are many melanin. On the contrary, Europeans and Americans have brown and other colors of hair. Because there is less melanin in hair. The number of cortical fibers also determines the thickness of hair. Hair pith, located in the center of hair, is a hollow cell aggregate containing some melanin particles. One or two rows of batteries are arranged side by side in a cubic honeycomb. There are countless pores in it. These inflatable holes have the function of heat insulation, which can improve the strength and rigidity of hair and hardly increase the weight of hair. Its task is to protect the head from direct sunlight.

Hair epidermis, hair cortex and hair medulla are also called epidermis, cortex and medulla.

If the epidermis and hair scales are not tightly closed or broken off, the hair will be dull (the reflectivity of light should be the highest in the case of plane)

Inside the cortex is the location of nutrients in the hair (including the color and straightness of the hair)

In fact, the medullary layer is basically not practical. People with thick hair exist, but people with thin hair do not necessarily exist.

But it plays an auxiliary role in theory, which is why people with thick and hard hair are more inclined to get their hair up ~

In fact, the best way to improve hair is to go to the hair salon for professional care every 4 weeks or so.

There are four kinds of chain bonds in hair: hydrogen bond, salt bond, disulfide bond and amino bond. Hair will break some hydrogen bonds in aqueous solution, so it will swell and soften in water and change its elasticity. When the hair dries, the hydrogen bonds are re-formed, and the hair will return to its original state. The traditional cold perm technology is to shape disulfide bonds through liquid medicine, so the hair after cold perm is curly when wet, and the curly hair will be elongated after drying. The purpose of thermoplastic ironing is to reduce and shape all four chain bonds, so it will curl slightly when dry than when wet.