Dry or dehydrated: clinical relevance of determining the etiology of dry skin

Antonina Smolka , microbiologist, virologist, methodologist at Christina company in Ukraine (Kiev)

If we take into account the classification of skin types, then dry skin is considered to be one that has hypofunction of the sebaceous glands. But during the cold season, complaints about dry skin come from patients whose sebaceous glands are normal or even increased, that is, with normal, oily or combination skin. And the cause of dryness in these cases is precisely dehydration. This leads to a well-known conclusion: it is clinically very important to distinguish between dry and dehydrated skin.

Dry skin type is characterized by decreased function of the sebaceous glands and insufficient amounts of epidermal lipids. This is an individual feature of the skin, which depends on genetics and the course of early development processes of the body. Such skin has impaired barrier functions, it is thin, atonic, dull, and prone to irritation. The only way to avoid unpleasant sensations and dermatological problems in this case is proper care and protection from adverse external factors.

In cosmetology, dehydrated skin is called skin with insufficient moisture. This is often associated with a violation of the horny barrier , as a result of which water is not retained in the layers. This condition can develop in patients with both dry and normal skin types, and even in those who have hyperfunction of the sebaceous glands. A striking example is dry seborrhea, which is mistakenly taken as an indicator of dry skin.

Also, skin with manifestations of cold dermatitis is often considered as dehydrated, the etiology of which is associated with a local immune reaction and does not consist in a moisture deficiency, but in a violation of the tone of the skin vascular wall and the subcutaneous fluid. To avoid diagnostic errors, it is necessary to accurately understand the reasons why the skin loses its ability to retain moisture levels at the proper level.

Who is responsible for dehydration?

Dehydrated skin is not a disease, but a pathological condition that develops against the background of a violation of the moisture content in the stratum corneum of the epidermis.

The stratum corneum is the thinnest barrier that separates the internal environment from the external one. It is responsible for protecting the skin and the entire body from the negative influence of the external environment. At the same time, it remains selectively permeable to water, gases and other substances.

The upper section of the stratum corneum is represented by rows of exfoliating “dead” anucleate epidermal cells - corneocytes, or horny scales. When corneocytes are rejected, the skin is cleared of exogenous agents - toxins, allergens and pathogenic microorganisms. At the border with the granular layer of the epidermis, the lower rows of cells in the stratum corneum have nuclei and are connected to each other by desmosomes. As cells differentiate and move toward the surface, cell membranes and desmosomes are transformed and then completely eliminated, and the intercellular spaces increase and are filled with dense layered lipid material.

The barrier function of the stratum corneum is largely determined by the physicochemical properties of its components - keratin, lipid matrix and hydrolipid mantle. The intracellular protein of corneocytes (keratin), due to its hydrophilic properties, ensures the structural integrity, stretching and elasticity of the stratum corneum.

Performing a barrier function, the stratum corneum regulates sweating and transdermal water loss. It is also the main obstacle to the penetration of harmful foreign agents into the body. This barrier separates the upper (dry) negatively charged stratum corneum and the moist, positively charged granular layer, separating the internal aqueous environment of the body from the gaseous external environment of the person.

Normally, the stratum corneum retains an amount of water sufficient to maintain its functions even with relatively low ambient humidity and a high evaporation rate. When the stratum corneum is damaged, excessive transepidermal water loss occurs and the effectiveness of the skin's natural moisturizing factor NMF (natural moisturizing factor), which is an integral part of the entire functional system of the intact epidermis, decreases.

The role of lipid structures

The lipid matrix (a system of intercellular epidermal lipids), filling the space between corneocytes, is an extended multilayer formation. The basis of the lipid matrix is a mixture of three types of lipids (ceramides, cholesterol and free fatty acids). The hydrophobic tails in ceramides are formed by polyunsaturated fatty acids (PUFAs), mainly linoleic acid. Ceramides of the stratum corneum contain PUFAs of varying lengths and degrees of saturation; they are better able to resist external factors attacking the skin, causing damage (oxidation) of their molecules.

The hydrolipid mantle is the first protective layer of the skin, the main component of which is sebum lipids, distributed in the form of a fatty film on the surface of the skin. Sebum secreted by the sebaceous glands gives the skin and hair elasticity, softness, water-repellent properties, regulates water evaporation, protects against excess solar radiation, takes part in thermoregulation, prevents the penetration of microorganisms from the external environment, etc. Sebum lipids differ in composition from epidermal - they consist mainly of neutral fats and waxes: triglycerides and their hydrolysis products, wax esters, cholesterol, and squalene. Thanks to the content of the latter in sebum, reliable adhesion of keratinocytes occurs, which ensures a high level of barrier properties of the skin.

Another important parameter characterizing the state of the hydrolipid mantle is the fluid content in the stratum corneum, since the stratum corneum of the epidermis contains only 10-15% water. The presence of a fluid supply contributes to the plasticity and extensibility of the stratum corneum.

Main causes of dehydrated skin

Normally, the stratum corneum retains an amount of water sufficient to maintain its functions even with relatively low ambient humidity and a high evaporation rate. When the stratum corneum is damaged, excessive transepidermal water loss occurs and the effectiveness of the skin's natural moisturizing factor (NMF), which is an integral part of the entire functional system of the intact epidermis, decreases.

Any disruption of fluid binding in the stratum corneum, caused by the action of exogenous toxins or endogenous factors, leads to disruption of the hydrolipid mantle and a decrease in lipid production on the skin surface, which is accompanied by an increase in transepidermal water loss.

Clinical picture of a patient with increased dry skin

Dehydrated skin looks dry, wrinkled, dull, lifeless, and loses its elasticity. There is a constant slight rejection of the cells of the stratum corneum in the form of the appearance of a large number of grayish-white scales on the surface of the skin. The surface of the skin becomes rough and hard to the touch. Cracks may appear in areas of constant tension. Often, manifestations of xerosis are accompanied by persistent redness and roughening of the skin. Its owner experiences pronounced unpleasant sensations in the form of tightness, tingling, itching.

In addition, with age, the total amount of water in the human body decreases, accordingly its amount in the skin decreases, and the blood supply in the dermis and epidermis deteriorates.

Correction methods

When one or more water-retaining structures are damaged, the water level in the stratum corneum drops. The choice of methods for restoring the hydrolipid balance will depend on the etiology of the problem - we will either increase the water content in the upper layers of the skin, or restore the barrier functions of the epidermis itself.

Now let's talk in detail about methods and preparations for restoring the hydrolipid balance of the skin.

Occlusion

The occlusive method will help slow down the evaporation of water from the skin and increase its content in the epidermis. In this case, cosmetics containing mineral oil, petroleum jelly, liquid silicones, lanolin, animal fats, squalene, and vegetable oils are used, forming a semi-permeable film on the surface of the skin, which only slows down, but does not completely block the evaporation of water.

Occlusive moisturizing creams quickly eliminate dry skin, reduce inflammation and itching in skin diseases, but they do not act on the cause of skin dehydration. They can be compared to crutches, which are necessary for those who cannot move independently, but are completely unnecessary for people with normal legs.

There are several categories of cosmetic products when the use of occlusive components is justified:

• post-peeling care products;

• baby cosmetics for skin care in the diaper area;

• protective hand creams.

Any moisturizing cream contains occlusive ingredients, only in some preparations they are the main ones, and in others they are auxiliary.

Hygroscopic preparations

The use of substances that can bind and retain water molecules is a great way to quickly moisturize the skin. There are two categories of hygroscopic compounds used in cosmetics. The first includes large polymer molecules that are unable to penetrate the stratum corneum. They attach to the surface of the skin, absorb moisture like a sponge, and form a “moist pillow”. These are sorbitol, hyaluronic acid, chitosan, polysaccharides, protein molecules and their hydrolysates (collagen and elastin).

But the use of these funds is not always justified. For example, in dry climates, when the relative water content of the environment is lower than that of the stratum corneum, the "cushion" begins to absorb water from the skin, causing the stratum corneum to become even drier.

The role of natural sponges in the stratum corneum is played by the components of the natural moisturizing factor - free amino acids, urea, lactic acid, sodium pyroglutamate. NMF molecules are located in proximity to corneocytes. A significant portion of the water present in the stratum corneum is associated with them. Water bound to sebum ensures the plasticity and smoothness of the skin surface. Unlike large molecules, NMF components can penetrate into the thickness of the stratum corneum and increase its moisture-retaining potential.

Substances that absorb and retain moisture in cosmetic products are usually combined with occlusive components.

Restoration of the hydrolipid barrier

In addition to using moisturizers that relieve the feeling of dryness and increase the moisture content in the stratum corneum, it is necessary to use products designed to restore the hydrolipid barrier. For this purpose, lipids are used - both in the form of pure oils and in combination with other ingredients. Lipid molecules penetrate into the intercellular spaces and are integrated into the lipid barrier, and some of the lipids gradually move along the intercellular spaces, reaching the living layers of the epidermis, and are included in cellular metabolism.

The restorative effectiveness and preferential mechanism of action of oils will depend on the lipid composition. Effective are lipid mixtures composed of physiological lipids - ceramides, cholesterol and free fatty acids.

A relatively new technology in cosmetics is the use of so-called lamellar emulsions based on phosphatidylcholine (lecithin), in which tiny droplets of lipids are stabilized not by conventional emulsifiers, but by a network of bilayers, similar to those that make up the lipid barrier. They have excellent moisturizing and regenerating properties, since they are compatible with the lipid barrier not only in composition, but also in structure.

You can slow down the process of dehydration and restore the stratum corneum of the skin, preventing it from becoming thinner, by acting on the dermis, activating the synthesis of glycosaminoglycans in it. This can be achieved through biorevitalization, mesotherapy, and hardware cosmetology.

Moisturizing is an essential part of the corneotherapy approach to skin care. Its essence is that it is enough to put the stratum corneum in order and maintain it to prolong the youth and health of our skin, help it cope with various skin diseases, alleviating discomfort.

Choosing a moisturizer is not an easy task, so you need to accurately determine the leading link in the pathogenesis of dry skin in each patient and, based on this, select a suitable moisturizer individually.

First published: Les Nouvelles Esthetiques Ukraine, No. 3 (67), 2011