Dry skin: Moistening to hydration

We hear complaints about dry skin quite often. The basis for such complaints can be arising after washing the tightness of the skin, roughness, painful microcracks. It would seem that nothing is easier - just apply a moisturizer on the skin, and the problem is solved!

Recall that one of the principal differences between the stratum corneum and other layers of the epidermis is the relatively low water content in it - about 15%. The horny layer (in which there are no living cells) a small amount of water is needed primarily in order to maintain plasticity and integrity (these cells of the stratum corneum differ from the cells of the deeper layers of the epidermis, which moisture is necessary for life). If, for one reason or another, the moisture content in the stratum corneum decreases, then its structure breaks down, which leads to a deterioration of the barrier properties. The latter means that the stratum corneum ceases to be an impenetrable barrier to water, and its evaporation intensifies.

As a result, there is a shortage of moisture in the living layers of the skin with all the ensuing consequences - a slowing of metabolism, the skin does not recover so quickly and heals, its appearance deteriorates noticeably (it fades and small wrinkles appear over time). In addition, through the broken barrier, microorganisms can penetrate more easily, causing, respectively, irritation.

How to properly moisturize the skin:

• Occlusion

Water continuously rises from the depths of the skin to its surface and then evaporates. Therefore, if its evaporation is slowed by covering the skin with something gas-tight, the water content in the epidermis will increase quite rapidly. This method is called occlusive (from English occlusion - obstruction, obstruction). If the film is completely impermeable (for example, polyethylene film), then the epidermis gets too much wet, which leads to the swelling of the stratum corneum and the destruction of the barrier. Rubber gloves and airtight clothing (in such cases it is said that "clothes do not breathe", ie does not pass gas) also lead to hyperhydration.

A semipermeable film that only slows down, but does not block the evaporation of water completely, will also eliminate the symptoms of dryness without damaging the skin. Ingredients that slow the evaporation of water include:

• mineral oil, petroleum jelly, liquid paraffin, ceresin - hydrocarbons, oil refining products;
• liquid silicones (sometimes called silicone oils) - silicone compounds;
• lanolin (from Latin lana - wool, oleum - oil) - animal wax, obtained by cleaning woolen wax (it is extracted with organic solvents from wool of sheep);
• animal fats - goose fat, whale fat (spermaceti), pork fat;
• Squalene and its squalene derivative (from the Latin squalus - shark) is a natural component of human sebum; sources of reception are different (for example, the liver of a shark, some plants);
• vegetable oils - mainly solid, for example shea butter (karite);
• natural waxes and their ethers - beeswax, vegetable waxes (coniferous, reed, etc.).

Due to the fact that Vaseline too moisturizes, it can slow down the restoration of the epidermal barrier - cells will not receive a signal in time that the barrier needs repair. Mostly occlusal (ie, blocking the evaporation of moisture) moisturizing creams quickly eliminate dry skin, reduce inflammation and itching in skin diseases, but they do not act on the cause of dehydration of the skin. They can be compared to crutches, which are necessary for those who can not move independently, but absolutely do not need people with normal legs. If the barrier function of the skin can not be restored, occlusal creams are necessary. If there is a chance of recovery, they should be used only at the initial stage.

• Moisture trappers

The use of substances that can bind and hold water molecules (such compounds are called hygroscopic) is a wonderful way to quickly moisturize the skin. In cosmetics, two categories of hygroscopic compounds are used, acting differently on the skin.

The method of "wet compress"

Large polymer molecules (more than 3000 Da) are not able to penetrate the stratum corneum. They are fixed on the surface of the skin and absorb moisture, like a sponge, forming something like a moist compress. Such an action is possessed by:

• glycerol;
• sorbitol;
• polyglycols (propylene glycol, ethylene glycol);
• polysaccharides - hyaluronic acid, chitosan, polysaccharides of vegetable and marine origin (chondroitin sulfate, mucopolysaccharides), pectins;
• protein molecules and their hydrolysates of animal and vegetable origin (in particular, the popular cosmetic ingredients collagen and elastin are included in cosmetics as moisturizing agents);
• polynucleic acids (DNA) and their hydrolysates.

The listed components are found in almost all cosmetic forms, including emulsion (creams). However, most of them in gels and "liquid" drugs (tonic, lotions, serums, concentrates).

And now attention: the use of moisturizing the skin like a "wet compress" is not always justified. For example, in a dry climate, when the relative content of water in the environment is lower than in the stratum corneum, the compress begins to "draw" water from the skin - as a result, the stratum corneum becomes drier. On the contrary, at high humidity of air application of cosmetics with the given components really softens and humidifies a skin. This improves the appearance of the skin - it acquires a matte shine, slightly tightened and smoothed.

• Deep moisturizing of the skin

On some cosmetics, they write that they have the effect of deep moisturizing of the skin. What does this mean? A common misconception is to think that all layers of the skin, including deep ones, are moisturized. In fact, only the horny layer is hydrated. The role of natural sponges in the stratum corneum is played by components of the natural moisturizing factor (NMF) - free amino acids, urea, lactic acid, sodium pyroglutamate. They are located throughout the stratum corneum, and only in it.

These compounds are formed as a result of the breakdown of proteins (mainly filagrinov), which ensure the adhesion of cells lying under the stratum corneum. Going to the stratum corneum, the cells not only lose the nucleus, the bonds between them also gradually break down (which is why unattached horny scales freely slough from the surface of the skin). NMF molecules are located in close proximity to the corneocytes. With NMF, a significant part of the water present in the stratum corneum is associated.

Bound water participates in the glueing of horny scales and along with sebum it ensures the plasticity and smoothness of the skin surface, however it does not prevent the disintegration of scales and their natural removal.

• Osmosis, or dilution effect

Deep hydration of the stratum corneum also has mineral substances (salts). The mechanism of action here is quite different. Penetrating the stratum corneum, salts increase its osmotic pressure. To restore the natural water-salt balance, the water from the underlying layers of the epidermis starts to flow into the stratum corneum and stay in it, as if diluting the aqueous phase and trying to bring the concentration of salt in it in accordance with the norm. The result is an increase in the hydration of the stratum corneum, i.e. Increase the content of water in it.

• Restoring the barrier

Even if the violation of the lipid barrier is not the primary cause of the development of dryness, it still occurs if the skin suffers from a lack of moisture for a long time. Therefore, in addition to the use of moisturizers, which remove the feeling of dryness and increase the moisture content in the stratum corneum, it is necessary to use the means designed to restore the barrier.

First of all, the damage in the barrier should be repaired rather quickly. To do this, lipids are used both in the form of pure oils, and in combination with other ingredients in the composition of local preparations. Molecules of lipids penetrate into the intercellular spaces and are built into the lipid barrier. Part of the lipid molecules deposited from above gradually moves along the intercellular spaces, reaches the living layers of the epidermis and is included in the cellular metabolism. In particular, they can serve as a substrate for the further synthesis of lipids, characteristic for the skin barrier.

Natural oils are mixtures of lipids. Therefore, the restoring efficiency and the predominant mechanism of the action of the oils will depend on their lipid composition. Oils containing essential fatty acids (linoleic and β-linoleum) promote the accelerated synthesis of the components of the lipid barrier, delivering the necessary lipid precursors directly to the cells (borage oil (borage), evening primrose, blackberry seed).

Oils rich in sterols stimulate keratinocytes and have anti-inflammatory properties (rosehip oil, taman, soybean, safflower). Oils enriched with saturated and monounsaturated fatty acids have more occlusal properties and contribute to the restoration of barrier properties due to the hydration of the epidermis (shea butter, sebaceous tree, macadamia, corn, coconut, cocoa, cashew).

Very effective lipid mixtures composed of physiological lipids - ceramides, cholesterol and free fatty acids. Physiological these lipids are called because they constitute the natural lipid barrier of the human stratum corneum. It has been experimentally found that the best reducing properties are their equimolar (ie in equal parts) mixture - "ceramides / cholesterol / free fatty acids" in the ratio 1: 1: 1.

[1], [2], [3]