Hyaluronic acid is an essential ingredient in anti-ageing products and a product for the hydration of the epidermis
Hyaluronic acid in the body:
Hyaluronic acid is an essential component of many tissues and physiological fluids. For example, the dermis contains half of the total hyaluronic acid in the human body. Isolated in 1934 by Meyer and Palmer, hyaluronic acid has long been considered as an uninteresting filler, but it now plays a decisive role in many physiological mechanisms:
- It is one of the main constituents of the extracellular matrix of the connective tissue, where it helps to maintain hydration thanks to its great capacity to retain water.
- It influences many important cellular processes: activation of macrophages and granulocytes, cell protection, proliferation, differentiation and migration.
Production of hyaluronic acid :
The first industrial production was carried out by extraction from a rooster’s crest.
|SOURCES||CONCENTRATION (HA mg/L)|
|Human Synovial Fluid||1420-3600|
|Human Chest Lymph||8,5-18|
|Human vitreous humor||140-338|
|Human Umbilical Cord||4100|
|Human amniotic fluid||20|
Table I: Concentration of hyaluronic acid in various tissues and fluids
In recent years, the production has shifted to biotechnologies, and much of the hyaluronic acid is now produced by fermentation. These biotechnologies make it possible to avoid the use of animal derivatives in cosmetics and pharmaceuticals.
Certain micro-organisms, in particular Lancefield’s streptococci A and C, are a source of hyaluronic acid. These lactic acid bacteria have the ability to produce hyaluronic acid, an essential component of their capsule. This extracellular production is in fact a natural defence phenomenon.
Whatever its origin, the chemical structure of the polymer is the same (identical molecule).
The ability of hyaluronic acid to retain water leads us to take a closer look at the phenomenon of hydration and the role of hyaluronic acid.
Water retention in the dermis:
The particular structure of hyaluronic acid allows it to retain more water than most other natural or synthetic polymers. Thus a 2% aqueous solution of pure hyaluronic acid retains the remaining 98% of water. This property is very specific to hyaluronic acid, and allows the formation of a viscoelastic network (gel structure).
One of the most important roles of hyaluronic acid in the skin is therefore to maintain hydration by retaining water in the extracellular matrix. Its polymer network then acts as a “molecular sponge”.
Hyaluronic acid in the epidermis:
Although the dermis contains most of the skin’s hyaluronic acid, epidermal cells also have the capacity to produce it.
Water retained by hyaluronic acid in both the dermis and the vital layers of the epidermis is essential for maintaining hydration.
Hyaluronic acid and ageing:
Skin ageing, particularly after the age of 50, is accompanied by changes in its macromolecular components, which lead to radical changes in the viscoelastic properties of the extracellular matrix of the dermis. In particular, the hyaluronic acid present in the epidermis gradually disappears. In the dermis, recent studies have shown that the major change is the increase in the bonds between the tissues and the hyaluronic acid, it becomes less and less extractable and loses its ability to retain water.
Consequently, it would seem that age-related skin alterations: loss of elasticity and suppleness, wrinkles, dryness, are linked to these changes in the hyaluronic acid network in the dermis.
Hyaluronic acid: a moisturizing cosmetic agent
High molecular weight hyaluronic acid solutions form non-occlusive viscoelastic films when applied to the skin. These films retain water in the same way as hyaluronic acid in the extracellular matrix of connective tissue. They also protect the skin from external aggressions, which could damage the lipid barrier of the epidermis and lead to significant desquamation of the stratum corneum.
In addition, the study of different moisturizers shows that the most effective polymer in maintaining hydration should have the following properties:
- A high molecular weight;
- A high affinity for water;
- A heterogeneous structure to form a soft, flexible film on the skin.
Hyaluronic acid, which meets all these criteria, is therefore an ideal moisturizer.
Hyaluronic acid: for multiple applications at the service of the skin
In conclusion, this multi-faceted molecule can be used in cosmetic products, food supplements and wrinkle-filling medical devices. However, different grades of hyaluronic acid are used depending on the applications.
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