Layers of skin

1st layer - horny

Formally, the stratum corneum is the topmost part of the layer called the epidermis. But in cosmetology, it is usually considered separately, since it is the target of most cosmetics. The stratum corneum is the thinnest film on the surface of the skin that can be lifted with a needle and that forms the wall of blisters when burned. If you put it under a microscope, you can see many translucent scales (horny scales, or corneocytes), which are built from a special protein - keratin. Horny scales were once living cells, but in the process of development they lost their nucleus and cellular organelles. From the moment a cell loses its nucleus, it formally becomes dead. The main task of these dead cells is to protect what is underneath them. In other words, they perform the same role as lizard scales or bird feathers. They just look less impressive.

The horny scales fit tightly together, connecting with special outgrowths on the shell. And all the space between the layers of horny scales is filled with a substance that is a mixture of lipids (fats). The intercellular substance plays the same role as cement masonry in a brick wall, i.e. it holds the horny scales together and ensures the integrity of the entire structure. Possessing water-repellent properties, the intercellular substance of the horny layer does not allow water and water-soluble substances into the skin, as well as does not allow excessive loss of water from the depths of the skin. It is thanks to the horny layer that the skin is a reliable barrier, protecting us from the external environment and foreign substances (we will talk about the skin barrier in more detail later).

Note that the substances included in cosmetics are foreign to the skin, since they do not belong to the body. Fulfilling its main task - to protect the body from any external influences, the skin is in no hurry to "accept" the stranger and tries not to allow the penetration of cosmetic components inside. Some cosmetics can destroy or weaken the protective layer of the skin, and then it will begin to lose moisture, and its sensitivity to environmental factors will increase.

No matter how strong the scales are and how well the "cement" holds them together, the trials that the skin is subjected to daily are so great that the stratum corneum wears out very quickly (just like clothes wear out). The way out that nature has found for this situation suggests itself - if the clothes are worn out, they need to be changed. Therefore, the worn-out horny scales fly off the surface of the skin and turn into ordinary household dust, which accumulates on bookshelves and under sofas (of course, not only our skin contributes to the formation of dust, but the skin's contribution is very large).

The stratum corneum is what we see when we look at the skin, and it is also the main point of action for cosmetics. However, its formation begins deep in the epidermis, and it is there that the processes that affect its appearance occur. By acting from the outside, we can decorate the stratum corneum, improve the properties of the surface (make it smoother and more flexible), and also protect it from damage. And yet, if we want to significantly change its structure, the action must begin from the inside.

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2nd layer - epidermis

The main task of the epidermis is to produce the stratum corneum. The life of the main cells of the epidermis, called keratinocytes, is dedicated to this goal. As they mature, keratinocytes move toward the surface of the skin. Moreover, this process is so well organized that the cells move upward in a single layer, "shoulder to shoulder."

The lowest layer of the epidermis, where continuously dividing cells are located, is called the basal layer. The rate of skin renewal depends on how intensively the cells of the basal layer divide. Although many cosmetics promise to stimulate the division of basal layer cells, in reality only a few are capable of this. And this is good, since in some skin conditions, stimulation of basal layer cell division is undesirable.

On the basement membrane between the basal keratinocytes are the cells responsible for pigment formation (melanocytes), slightly higher are the immune cells responsible for recognizing foreign substances and microorganisms (Langerhans cells). Obviously, products that penetrate deeper than the stratum corneum will affect not only the keratinocytes, but also the immune system cells and pigment cells. Another type of cell found in the epidermis, the Merkel cells, are responsible for tactile sensitivity.

3rd layer - dermis

The dermis is something like a soft mattress on which the epidermis rests. The dermis is separated from the epidermis by the basal membrane. It contains blood and lymphatic vessels that nourish the skin, while the epidermis is devoid of vessels and is completely dependent on the dermis. The basis of the dermis, like the basis of most mattresses, is made up of "springs". Only in this case, these are special fibers built from proteins. Fibers consisting of the protein collagen (collagen fibers) are responsible for the elasticity and rigidity of the dermis, and fibers consisting of the protein elastin (elastin fibers) allow the skin to stretch and return to its previous state. The space between the "springs" is filled with "padding". It is formed by gel-like substances (mainly hyaluronic acid) that retain water. Although the dermis is partly protected from external influences by the epidermis and the stratum corneum, damage nevertheless gradually accumulates in it. But this happens rather slowly, since all structures of the dermis are constantly renewed. If the renewal process went equally well throughout life, the skin would always remain fresh and young. However, as the body ages, all renewal processes in it slow down, which leads to the accumulation of damaged molecules, a decrease in the elasticity and flexibility of the skin, and the appearance of wrinkles.

Between the fibers are the main cells of the dermis - fibroblasts. Fibroblasts are biosynthetic factories that produce various compounds (components of the intercellular matrix of the dermis, enzymes, signal molecules, etc.).

The dermis is not visible from the outside. But the condition of its structures determines whether the skin will look elastic or flaccid, whether it will be smooth or wrinkled. Even the color of the skin partially depends on the dermis, since the skin gets its blush from the blood that runs through the vessels of the dermis. With atrophy of the dermis and epidermis, the skin acquires a yellowish color due to the translucent subcutaneous fat.

4th layer - adipose tissue

Adipose tissue, as its name suggests, contains fat. And it is supposed to be where it is. Everyone has probably heard the admiring assessment of a slender girl - "she does not have a gram of fat." However, if this were true, the girl would be a pitiful sight. In reality, there is no beauty without fat, since it is adipose tissue that gives forms roundness, and skin - freshness and smoothness. In addition, it softens blows, retains heat and at certain periods of a woman's life helps in the synthesis of female sex hormones. Adipose tissue consists of lobules separated by fibrous tissue. Inside the lobule are fat cells, similar to bags of fat, and blood vessels also pass through. Any disturbances in the quality of adipose tissue - accumulation of excess fat in cells, thickening of the partitions between the lobules, swelling, inflammation, etc. - have a catastrophic effect on appearance.

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