Skin moisture – a complex phenomenon

The level of moisture in the skin reflects the balance between the amount of water that reaches the skin through blood flow and general metabolism, and the amount of water that evaporates from the surface of the skin.

The water that reaches the dermis layer through the blood circulation permeates through all the layers of the skin on its way out, to the surface area of the skin.

How the skin maintains its water content

Some of the water is found in the dermis, where it is tightly bound to GAG – (glucose-amino-glucan) molecules. These molecules have strong hydrophilic properties (ability to connect to water), and together with the elastin and collagen molecules they make up the substance that protects the cells and forms the support tissue of the skin.

At the level of the epidermis, water is stored in the cells of the stratum corneum of the skin using the NMF (NATURAL MOISTURIZING FACTOR ). The NMF consists of hydrophilic molecules and mainly sugars, mineral salts, and 40% free amino acids. In the more outer part, the water binds to the aqueous components of the hydrophilic membrane, which covers the stratum corneum.

Skin moisture condition

The skin moisture condition depends on the balance between water that comes from food and evaporation from the surface of the skin. When the supply of water coming from the blood circulation replaces the amount of water that evaporated out – the skin maintains normal moisture. When the loss of water through the epidermis (outside) is increased, the balance is disturbed, and the skin suffers from dryness. The moisture condition also depends on the ability to bind water from the air to the stratum corneum. The NMF found in the keratin fibers of the cells of the stratum corneum, captures and fixes the “external” water found in the moisture in the air or in skin care products. Therefore, a healthy stratum corneum is an important factor in maintaining skin moisture, and any damage to it reduces the ability to absorb external moisture or prevent internal moisture from evaporating.

The causes of skin dryness

Damage to the integrity of the stratum corneum

The stratum corneum is made up of cells with cement-like intercellular material between them. This “cement” consists of several types of oils (lipids) organized in a permanent two-layer structure. The cement is largely responsible for the stratum corneum being an impermeable layer. In case of damage to its integrity, the impermeable structure is destroyed and thus the loss of water through the epidermis is possible, as it happens in a strainer. Increased moisture loss causes dryness in the skin and the damage to the stratum corneum contributes to the rough appearance characteristic of dry skin.

Damage to the moisture retention mechanism

The stratum corneum is able to bind water in an amount reaching up to 9 times its weight. This ability is mainly achieved through the NMF. If the corneum cell membrane is damaged by a mechanical (rubbing) or chemical (cleaning) factor, the NMF components leak from the cells, thus reducing their ability to store water. This is why cleaning the skin with strong soap is not recommended.

Breaks in the hydrophilic barrier

The hydrophilic barrier is a sealed natural membrane that covers the entire epidermis, reducing the evaporation of water from the surface of the skin. This layer consists of an aqueous phase and a fatty phase containing lipids secreted from the epidermal cells.

The operation of the hydrophilic barrier has not been studied in depth, but it is likely that this membrane reduces the evaporation of water from the surface of the skin and contributes to preventing the development of disease-causing bacteria.

This membrane may be damaged for various reasons such as a disease that affects the metabolism of the skin, or random factors such as aggressive cleaning.