What are the signs of dehydrated skin?
Dehydrated skin appears as a lack of radiance and comfort with intense, persistent tightness. The skin feels itchy, especially after washing and also has scales. This is an unusual, temporary state that is not necessary related to a “dry” skin type. This means oily skin can easily have times when it is dehydrated.
What causes skin dehydration?
Water, just like air, is an element essential to life. Water accounts for approximately 65% of an adult’s total body weight. Thus, a person weighing 70 kg is made up of around 49 litres of water, 15% of which are concentrated in the skin. Water plays an essential role in the skin. The skin is a reservoir that other organs tap into. It facilitates exchanges with the exterior environment: water moves from the dermis to the surface by impregnating the various layers by diffusion. This flow of water is called Transepidermal Water Loss (TEWL). Naturally protected by a hydrolipidic film on its surface, the horny layer (outer layer of the epidermis) curbs this evaporation process. If this physiological barrier is impaired, TEWL speeds up, thus making the skin dry. Water in the dermis no longer circulates to the epidermis; the hydrolipidic film stops functioning properly. All sorts of factors can cause dehydration:
. Environmental factors such as cold, winter, wind, pollution, UV rays, etc.;
. External factors such as tobacco or alcohol;
. Emotional factors, stress or fatigue;
. Certain medical treatments, such as anti-acne or anti-cholesterol medications; and
. Cosmetic products that are too aggressive, detergent, stripping or drying.
How is water regulated in the skin?
The skin is very sensitive to water deficiencies, that’s why it has a hydroregulation mechanism.
1) Skin hydroregulation
The skin is 70% water. Nearly 75% is located deep down in the dermis where it plays an important role in the skin’s resistance. Two elements moisturise the epidermis: static water, which is fixed, and dynamic water, which circulates. Hydroregulation achieves a balance between these two aqueous components and it alone guarantees the skin’s physical and functional integrity. Three main factors contribute to hydroregulation: NMFs (Natural Moisturizing Factors), lipids in the horny layer and aquaporins.
2) NMFs (Natural Moisturizing Factors), hydroregulation factors
NMFs are molecules that can bind water within the horny layer; they are called humectants. The most commonly known NMFs are urea and lactic acid. Other substances used in cosmetics have the same properties; these include glycerine and xylitol.
Water and the Skin’s Barrier Function
The horny layer is made of cells without nuclei that are “cemented” by lipids called intercorneocyte lipids. The right quantity and quality of these lipids is necessary for the horny layer’s integrity and therefore its “barrier” function. When they are lacking or deteriorating, cellular cohesion is no longer guaranteed. The result is an increase in perspiration, also called Transepidermal Water Loss (TWL: permanent, light and natural evaporation of the water found in the body). Well-hydrated skin should be capable of retaining its water, hence the importance of the inter-corneocyte lipids.
What are aquaporins?
Aquaporins are the channels through which water moves in the epidermis. These proteins are made by the keratinocytes (epidermal generating cells) and inserted in their membrane to allow water molecules to pass through. This movement is essential to the skin. The epidermis is not vascularised. All elements required for cellular life (mineral salts, vitamins, nutritional elements, etc.) that are carried by the blood to the dermis reach the surface layers of the skin thanks to aquaporins. Without aquaporins, the epidermis would not be able to “feed” itself.
How can you tell the difference between dry skin and dehydrated skin?
Dehydrated skin is always a temporary condition that can be reversed with appropriate products. It is an alteration in the superficial layer of the epidermis that lacks water. This lack of hydration disturbs the skin’s barrier function and leads to discomfort. On the other hand, dry or very dry skin is a permanent condition that describes a particular skin type that is lacking both water and lipids.
Who is affected?
All skin types can become dehydrated in certain circumstances or during particular seasons.