Skin protection: epidermal-lipid layer. The lipid layer of the skin: what is it and how to restore after winter Skin lipid barrier cosmetics
Used in medicine and cosmetology, the name of the lipid structures of the stratum corneum of the epidermis, designed to emphasize their barrier (protective) function.
The main task facing the barrier is to ensure the integrity of the skin. Bacteria, viruses and other exogenous substances, as a rule, enter the body through the intercellular spaces of the stratum corneum. These gaps cover the lipids.
The lipids of the stratum corneum has nothing to do with sebum. They differ in composition, structure, and origin. Sebum is produced in the cells of the sebaceous glands. The stratum corneum lipids are synthesized in keratinocytes as they mature. At the level of the transition of the granular layer to the stratum corneum, these lipids (more precisely, their precursors) are released into the intercellular space, where, with the participation of enzymes, the enzymatic assembly of lipid layers (membranes) begins. The lipid barrier of the stratum corneum consists of several such extended and continuous layers superimposed on each other. Between the layers are water molecules that are in constant motion, moving from the lower to the upper layers, and evaporate when they reach the surface of the skin.
The lipid barrier consists of three types of lipids: ceramides, free fatty acids and cholesterol.
Ceramides(sphingolipids) form the basis of the lipid layer between the horny scales. These are complex lipids, consisting of several blocks - fatty alcohol sphingosine or phytosphingosine (forms a hydrophilic "head") and one fatty acid (lipophilic "tail"). Among ceramides, long-chain type 1 ceramides, which include linoleic acid, stand out. These ceramides pierce adjacent lipid layers and bind them into a single structure. With a lack of linolenic acid, the synthesis of ceramides 1 suffers, respectively, the lipid layer of the stratum corneum loses its integrity and disintegrates. The consequence of this is dry skin and other symptoms associated with it (flaking, hypersensitivity, irritation, etc.).
Fatty acid are present in the lipid barrier of the stratum corneum both in the composition of ceramides and in the free state. An important characteristic of fatty acids is their saturation, i.e. the presence of double bonds. Fatty acids containing one unsaturated bond are called monounsaturated, two or more - polyunsaturated. The quantity and quality of unsaturated fatty acids (both free and included in complex lipids) determines the viscosity of the fatty medium (the more polyunsaturated fatty acids, the more liquid it is). To maintain the integrity of the lipid layers of the skin and their physical and chemical properties, the right balance between saturated and unsaturated fatty acids is necessary.
Cholesterol- an important component of not only the lipid barrier of the stratum corneum, but also the membranes of all living cells. Unlike ceramides, cholesterol does not have a hydrophilic site and is a lipophilic molecule. It is localized between hydrophobic tails and does not come into contact with water. Cholesterol regulates the viscosity of the lipid membrane and helps maintain its integrity and continuity.
Literature:
1. Grabeklis S.A. DMAE and (myo) fibroblasts. Mesotherapy 2009; №6-7
2. Deev AI How to overcome the horny shield of our skin? Mesotherapy 2010; №10 / 02
3. Zorina A., Zorin V., Cherkasov V. Dermal fibroblasts: diversity of phenotypes and physiological functions, role in skin aging. Aesthetic Medicine 2012; volume XI; #1
4. Nino M., Calabro G., Santoniani P. Non-invasive transdermal delivery of active substances: practical use and promising developments. Cosmetics & Medicine 2010; #4
The skin is the outer covering of the human body, carrying out its relationship with the environment. The skin is the largest organ of the human body, multifunctional and extremely complex in structure. It performs many functions, and the performance of these diverse functions takes place in constantly changing, often harsh and aggressive conditions under the influence of various environmental factors. What is the structure of human skin, and what is the role of the lipid layer?
Skin structure: the life cycle of keratinocytes
The unique structure of the skin provides the above functions. The skin is made up of three layers: epidermis, dermis, and subcutaneous fat. Each of them has a special structure. Only the epidermis is available for direct exposure to cosmetics, and mainly its stratum corneum.
The main cell of the epidermis is the keratinocyte. The lowest layer of the epidermis is called the basal; keratinocytes of this layer are in a state of constant division. As they mature, keratinocytes move up to the surface of the skin, and the cells move in a single layer, which makes it possible to single out separate layers in the epidermis depending on the stage of development, or rather, on the stage of “dying” of keratinocytes.
The main functions of the skin:
- barrier;
- protective;
- thermoregulatory;
- receptor;
- endocrine;
- excretory;
- respiratory;
- immune;
- vitamin-forming;
- social.
What is the lipid barrier of the skin?
The upper layer of the epidermis is called the horny and is represented by corneocytes - cells that are filled with keratin protein and have lost the nucleus, as well as cell organelles. The sheath of corneocytes is called horny envelopes. They have the shape of a hexagon, fit tightly to each other, connecting with special protrusions - corneodesmosomes.
The space between corneocytes is filled with a lipid-protein structure (the so-called lipid barrier of the skin), which “glues” the corneocytes together. This structure of the skin ensures the integrity of the stratum corneum. The lipids of this barrier consist of ceramides, cholesterol and its esters, and free fatty acids.
Healthy skin with good barrier properties is characterized by a ceramide/cholesterol/free fatty acid ratio of 1:1:1. A change in this proportion leads to a violation of the entire structure of the lipid barrier and, as a result, to a weakening of the barrier function of the stratum corneum as a whole.
The lipid barrier is formed by alternating layers of lipids and water.
What are the functions of the layers of the skin
Despite the fact that the stratum corneum consists of dead cells, it is metabolically active due to the work of numerous enzymes. The stratum corneum is a reliable barrier to the path of various substances. The corneocytes themselves are practically impermeable, the passage of substances is possible only through the lipid layer. This layer is impermeable to water-soluble compounds, and the passage of large molecules (for example, proteins or polysaccharides) is also difficult. The structure of the skin, in particular the stratum corneum, provides selective permeability of the skin for various substances.
The epidermis and dermis are permeated with free nerve endings that have special receptors for histamine and are highly sensitive to it.
Histamine is secreted by mast cells with the most minor changes in the extracellular environment. The result is an itching sensation. This structure of the skin provides an immediate reaction of the skin to the allergenic agent.
By blocking the penetration of water-soluble compounds, the stratum corneum also effectively protects the skin from excessive moisture loss, that is, from dehydration. Fat-soluble compounds not only pass through the epidermal barrier, but can also change its permeability to other substances. To increase the permeability of lipid layers, unsaturated fatty acids are added to the composition of external medicinal and cosmetic products, which are embedded in the lipid layer and reduce its viscosity.
It is important for cosmetologists and dermatologists to know the structure of the skin in order to understand the ways and means of eliminating skin problems without harming its cells.
The lipid barrier of the skin is the part of the epidermal barrier that first contacts the environment. This is a unique mechanism that allowed a person in the course of evolution to defend himself from the often aggressive environment.
The stratum corneum of the epidermis consists of 10-25 layers of cells oriented parallel to the surface of the skin and immersed in the lipid matrix (lipid barrier of the skin). It is the cells of the stratum corneum of the epidermis and the lipid matrix that fills the intercellular spaces that provide the barrier functions of the skin, protecting the body from the penetration of bacteria, viruses and other exogenous substances, as well as retaining water and electrolytes.
The lipid matrix of the stratum corneum of the epidermis makes up about 10% of its volume and has a unique structure and chemical composition.
Chemical composition of the lipid barrier of the skin
The lipids of the epidermal barrier of the skin are mainly composed of:
- ceramides (50%);
- cholesterol and its esters (25%);
- saturated fatty acids (10%).
A balanced ratio of these three categories of lipids is essential to ensure the integrity and protective properties of the lipid barrier of the skin.
Ceramides- This is the simplest type of sphingolipids, consisting of sphingosine and a fatty acid (in particular, linoleic). Currently, 342 ceramides have been identified in the stratum corneum of the epidermis, belonging to 12 different types. Their list is constantly updated.
Ceramides perform great amount biological functions. One of the most important is structuring (ceramides are able to form bilayers).
Cholesterol is one of the most important lipids that form the lipid barrier of the skin. Basically, it is synthesized directly in the epidermis. A small amount of it can come directly from the bloodstream.
The main function of cholesterol as a component of the epidermal barrier is to impart plasticity to the lipid matrix. Without it, the stratum corneum of the epidermis would be very fragile.
Concerning free fatty acids, then saturated fatty acids dominate in the stratum corneum of the epidermis, and long-chain fatty acids predominate. Most of them are synthesized in the body itself. Some acids (for example, linoleic, gamma-linolenic) enter the body only with food.
Free fatty acids also play a structuring role.
Lipids in the intercellular spaces of the stratum corneum are organized in the form of plates collected from 3 layers (wide - narrow - wide). The wide layer is paired bilayers of ceramides and cholesterol, the narrow one is one unifying layer of ceramides.
The formation of a bilayer of ceramides is due to the fact that they turn their nonpolar part towards each other, and the polar part outward. This is a unique quality of ceramides, which determines the barrier properties of the epidermis.
Placed in this way, ceramides essentially "stitch" the layers. Due to this, in a plane perpendicular to the plates, lipids are organized into a rigid rectangular crystal lattice.
Figuratively, such a system of organization of the lipid barrier of the skin can be described as a quilt 🙂 Lipid layers are stitched with ceramide chains. Similarly, lipid layers are "sewn" to the cells of the stratum corneum of the epidermis, ensuring the integrity of the epidermal barrier of the skin.
For the correct structural organization of the lipid barrier of the skin, the chemical composition of lipids, the ratio of the main components, is very important. If this balance is disturbed, the stratum corneum of the skin becomes unable to perform its protective functions.
Why is the lipid barrier of the skin destroyed?
Many factors can provoke the destruction of the lipid barrier of the skin:
- any mechanical damage to the skin (wounds, burns, frostbite, cuts, scratches);
- skin diseases (acne, atopic dermatitis, psoriasis, etc.);
- exposure to ultraviolet radiation (see "Photoaging") and other environmental factors (frequent showering, swimming pool visits, dry air from heating systems, cold air);
- exposure to aggressive surfactants in cleansers, shower gels, shampoos, etc.;
- metabolic diseases with impaired lipid synthesis;
- decrease in cholesterol synthesis in the epidermis with age;
- constant contact with chemicals (for example, with chemical detergents);
- psychological stress (hormones synthesized during stress negatively affect the epidermal barrier);
- oxidative stress - damage to the intercellular structures of the stratum corneum of the epidermis by free radicals (see "Lipid peroxidation", "Antioxidants and skin");
- unbalanced diet (lack of fatty acids).
Such a number of provoking factors in Everyday life leads to the fact that every day we gradually remove its natural protective barrier from the skin.
The skin is trying to replenish the content of lipids (they are in stock in the "pantries" of the skin - lamellar bodies), but its possibilities are not unlimited. It takes time for the synthesis of new lipids in the skin. If the protective barrier of the skin during this period is affected by other adverse factors, then it is not able to fully restore itself, and as a result, external signs of the destruction of the lipid barrier of the skin appear.
How is the destruction of the lipid barrier of the skin manifested?
If this structure is violated, the barrier ceases to partially or completely cope with its task - primarily to preserve water in the body and protect against the penetration of harmful substances and microorganisms.
The first sign of the destruction of the lipid barrier of the skin is dehydration of the skin due to increased evaporation of water. Dehydrated skin ages quickly, loses firmness and elasticity. Dry skin, peeling, fine wrinkles appear.
The skin becomes sensitive, vulnerable to external factors. The destruction of the barrier that protects against the penetration of bacteria and viruses leads to irritation, development inflammatory processes in the skin (eg, acne), skin diseases.
This situation requires urgent measures to restore the lipid layer of the skin:
- termination of exposure to factors that provoke the destruction of the epidermal barrier;
- the use of creams containing physiological lipids (ceramides, free fatty acids and cholesterol) in a balanced combination.
We will talk more about ways to restore the epidermal barrier in the article “Restoring the lipid barrier of the skin“.
Our skin needs protection from dehydration, bacteria, viruses and other irritants. It is the lipid layer that performs the protective function. When the lipid layer is broken, wrinkles appear on the skin, it becomes dull and unkempt, which means that as a result you will look older than your years. How to prevent this - says Feelgood.
What is a lipid layer and why is it needed
The outer layer of the epidermis is called the stratum corneum. It received this name thanks to appearance their cells - they are spiked and look like horns. In the cells of this layer there are no nuclei, but only the protein keratin. It is the stratum corneum that performs a protective function and protects our skin from exposure external environment and dehydration. The surface of this layer is covered with a water-lipid layer. The lipid layer is a mixture of sebum, sweat and exfoliating particles of the stratum corneum. At first glance, it may seem that this is something unhygienic, but in fact it is a very necessary component for our skin, and indeed for the whole organism. The lipid layer is so arranged that it does not allow various substances to penetrate into the skin. harmful substances outside, but perfectly passes oxygen.
How is the lipid layer damaged?
- Washing your face with soap hot water or poor quality cleansers and skin care products;
- An abrupt change in temperature also disrupts the lipid layer. For example, in winter from frost to a heated room;
- Visiting the solarium, sunbathing in unlimited quantities;
- Due to physical stress, the production of lipids by the body is also disrupted (strong friction of the face with a towel after washing)
How to restore the lipid layer
Damaged lipid mantle not only leads to dehydration, but in addition, our skin becomes sensitive to the effects of various negative factors on it. The use of oils does an excellent job of restoring the lipid layer, since the main components of the lipid barrier are ceramides, cholesterol, free fatty acids and phospholipids. Properly selected natural oils, due to their similar composition, can help restore both the artificial lipid layer and the real one. IN natural oils a large number of natural fatty acids and phospholipids. In addition, the phytosterols contained in the oils tend to replace the natural cholesterol of the stratum corneum. The oils also contain antioxidants that prevent the oxidation of skin lipids. The best of the oils for restoring the lipid layer are linseed, burdock, and oil from grape seed. These oils can even be used for oily skin. It is best to apply the oil on the skin before going to bed, then pat your face dry after 10 minutes. paper napkin. If your skin is too oily in the morning, rinse your face with water at room temperature (but not hot!). You should apply the oil every day before going to bed for a month, and after this time you will notice how your skin acquires a healthy glow, shine, and dehydration and dryness no longer bother you!
