Water and skin health
Skin well-being plays a vital role in maintaining health, and its care is a priority for mankind, in all historical periods. The main function of the skin is to protect the body from exogenous substances and excessive water loss.
Water is an indispensable element for the well-being of the skin, whose cleansing and hydration are fundamental to keep it in good condition.
Skin hydration
Water follows a well-defined path within the different skin layers: from the bloodstream it reaches the dermis, and then spreads regularly and constantly up to the upper layers of the epidermis, where it has the task of preserving skin hydration . The natural hydration of the skin is the result of different biological mechanisms with specific functions, which take place at the level of the dermis, epidermis and stratum corneum.
Epidermis and Acid Mantle
The water present in the epidermis comes from the underlying dermis; the mechanism of regulation of the water flow that crosses the basement membrane has not yet been clarified. However, proper hydration of the epidermis and the stratum corneum is only possible if the water supply from the dermis is sufficient to balance the insensitive losses and if the capacity of water repellency of the upper compartments of the skin is efficient and constant. The aqueous film that covers the epidermis is usually defined as " acid mantle ", with reference to its weakly acid pH (around 5.5); it is arranged almost continuously on the surface of the stratum corneum and is made up of a set of substances of different origin.1 Its composition is mainly characterized by the secretion products of the eccrine sweat glands and of the sebaceous glands, from polypeptide aggregates coming from the decay of the corneocytes, from purine and glucidic substances deriving from the denucleation of keratinocytes, and from lipids of epidermal origin. In summary, it is a mixture of lipophilic and water-soluble substances, whose job is to protect the skin and, in particular, to keep the horny state hydrated. This surface film is divided into two parts : the first is defined as a surface lipid film and includes both sebum and epidermal lipids; the second is defined as NMF ( natural moisturizing factor ) and is composed of all the non-lipid substances present on the epidermal surface. Even today the mechanisms with which the stratum corneum and the constituents of the epidermis are able to regulate the water content of the skin are studied in depth. In fact, cosmetic research has highlighted new mechanisms, and we try to understand which new molecules can be developed to modulate the mechanisms brought to light. Recent data show that the movement of water between the cells in the different levels of the epidermis depends on specific proteins called aquaporins. 2
aquaporins
The aquaporins are proteins present in the epidermis that form channels designed to convey water and water-soluble ingredients, transporting them to the surface.Aquaporins are essential in regulating the water content of the skin. In 2003, for this overwhelming discovery, Peter Agre, an American biochemist, was awarded the prestigious Nobel Prize in Chemistry. Before this revelation it was believed that the water crossed the membrane only by simple diffusion. Aquaporins are a family of integral membrane proteins with a water carrier function, and their physiological implications go far beyond the skin compartment, as they are present in many tissues of our body.
In these years, aquaporins have been studied to understand how they work, what their role inside the skin is and, above all, how it is possible to stimulate their synthesis. However, it has only recently begun to design the development of specific peptides, capable of stimulating the synthesis of aquaporins, and useful for improving the water balance of the skin.
Dermis and glycosaminoglycans
At the level of the dermis, water is retained by the body thanks to the presence of glycosaminoglycans (GAGs), hydrophilic polymers capable of fixing large amounts of water at the level of the extracellular matrix. The dermis is particularly rich in water: it contains about 70% of the water supply of the entire skin, a concentration that is hardly detachable by external events but mainly dependent on the state of hydration of the entire organism and on the efficiency of protein synthesis by fibroblasts. In cases of systemic dehydration, the dermal reserve becomes the first source from which to draw to make up for water shortages. Another cause of impoverishment of the dermal reserve is attributable to the qualitative and quantitative alteration of the molecules responsible for binding water: the typical case is chronic photodamage, in which the dermal structures are altered by UV radiation and lose their capacity to hold it.
