Hyaluronic Acid is a hydrophilic molecule (a substance capable of binding with water and retaining it) that possesses the ability to retain up to a thousand times its weight in water. The different molecular weights intervene at a different level of the epidermis, guaranteeing a conspicuous supply of water, thus reducing the phenomenon of evaporation and favouring the physiological production of collagen, a protein indispensable to the tissues to maintain the turgidity and elasticity typical of youth.
Size and molecular weight
Hyaluronic acid can weigh millions of Da (Da=Dalton, a measure of molecular weight).
To give an idea of size, a 10 million Dalton molecule of hyaluronic acid in human tissue is 1 nm thick, 2.5 cm long and consists of 25000 repeated units.
Typically, the mass of a hyaluronic acid molecule is around 4 million Daltons, has more than 10,000 repeating units and takes on a tangled shape. It can bind to other hyaluronic acid molecules to form a kind of ‘network’.
The molecular weight of sodium hyaluronate can range from 2.2 mDalton of the largest molecules to 3/10 kDalton of molecules with a lower weight.
Behaviour in water
Hyaluronic acid is very poorly soluble in water unless it is converted to the ionised form, stabilising it at neutral pH (approx. pH7) and thus giving rise to Hyaluronate, which is instead water-soluble. For this reason, sodium hyaluronate, that is hyaluronic acid converted to a saline form to make it water-soluble, is usually used for cosmetic use. In aqueous solution, sodium hyaluronate forms stable tertiary structures (network-like) and can assume different configurations that influence viscosity.
The factors influencing the viscosity of sodium hyaluronate solutions are:
- Size, molecular weight and chain length (they are all related): as they increase, the network becomes denser and viscosity and viscoelasticity increase.
- PH: if the pH is lower than 4 or higher than 11, it is hydrolysed (fragmented) and therefore becomes less viscous (more liquid, in other words).
- Electrolyte concentration: if it increases, the viscosity decreases.
- Concentration of sodium hyaluronate: if the concentration increases, the network becomes denser and the viscosity increases.
- Temperature: if the temperature increases, the sodium hyaluronate breaks up and the viscosity decreases.
Sodium Hyaluronate can be used in different molecular weights:
- Sodium Hyaluronate HMW – High Molecular Weight: sodium salt of Hyaluronic Acid with a high molecular weight (1,500-1800 kDalton) for moisturising, filming and soothing action. It forms an elastic film on the skin that keeps it moisturised and slows or prevents TEWL (Trans-Epidermal Water Loss), thus ensuring daily and long-term moisturisation. In 1% solution it creates a dense gel.
- Sodium Hyaluronate MMW – Medium Molecular Weight: sodium salt of hyaluronic acid with a medium molecular weight (300-800 kDalton) for moisturising, long-lasting and anti-wrinkle action. Thanks to its molecular weight it can partially penetrate the epidermis, moisturises in depth, promotes the absorption of nutrients and the regenerative processes of the epidermis, increasing its elasticity and delaying the appearance of signs of ageing. In a 1% solution it creates a gel with a medium/low viscosity.
- Sodium Hyaluronate LMW – Low Molecular Weight: sodium salt of low molecular weight hyaluronic acid (50-200 kDalton) with anti-wrinkle, repairing and regenerating action. Thanks to its low molecular weight it penetrates the dermis, promotes the absorption of nutrients and the regenerative processes of the epidermis, increasing collagen and elastin production and speeding up cell turnover. It slows the appearance of signs of ageing and reduces their formation. In a 1% aqueous solution it does not create a gel, it only makes the water slightly more viscous to the touch.
- Sodium Hyaluronate VLMW – Very Low Moleculr Weight: Hydrolysed Hyaluronic Acid with a very low molecular weight (10 kDalton). Thanks to its molecular weight, it is able to penetrate the epidermis and interacts with the cell metabolism by increasing the production of endogenous hyaluronic acid, ensuring deep hydration and stimulating tissue regeneration. It rejuvenates the skin by increasing its viscoelastic properties and reduces the appearance of wrinkles and classic periocular ‘crow’s feet’. It has a solubility of 10% in water. In a 1% aqueous solution it does not create a gel.
In cosmetic formulations, the use of high molecular weight sodium hyaluronate creates a film on the skin, preventing water loss (TEWL Trans-Epidermal Water Loss) and increasing hydration; conversely, formulations containing low molecular weight sodium hyaluronate (200 – 1,000 kDalton) allow absorption of the molecule down to the deepest layers of the dermis (due to its reduced molecular size), thus providing deep hydration and improved skin tone and elasticity. Medium molecular weight sodium hyaluronate, on the other hand, is responsible for water retention in the medium/superficial layers of the epidermis, completing the moisturising and toning action obtained in synergy with the low and high molecular weight molecules.
Why use it?
In an individual weighing 70 kg, there are about 15 g of hyaluronic acid and about a third of this is degraded and resynthesised every day. Over the years, the presence of hyaluronic acid in the skin diminishes (at 50 years of age, for example, only half of the original genetic capital remains), so the ability of the skin to retain fluids decreases, and the skin’s own ability to remain relaxed and elastic also decreases. Applying hyaluronic acid topically helps support collagen synthesis.
Moreover, being a substance produced naturally by the body, the skin can absorb it very easily. The application of hyaluronic acid helps to diminish the signs of ageing and at the same time manages to keep the skin adequately hydrated. It is non-allergenic as its structure is identical in all species.
Gen-Hyal serums are developed using the most suitable molecular weight in relation to the intended activity.
Gen-Hyal Plus – Hyaluronic acid in HMW at a real concentration of 0.5%: Long-term moisturising action, slowing down water loss in the tissues. Recommended for daily use or as a booster for other cosmetic creams.
Gen-Hyal Premium – Hyaluronic acid in double molecular weight HMW and MMW in real 2% concentration: combines the moisturising and filming (protective) action of the high molecular weight with the deeper action of the medium weight. Moisturising, anti-ageing and protective. Indicated for more mature skin.
All Gen-Hyal products contain Hyaluronic Acid but the two serums described above are pure aqueous solutions.
Gen-Hyal Elargan – 1% Hyaluronic Acid in double molecular weight (HMW and MMW) combined with nourishing and elasticising active ingredients such as argan oil.
Gen-Hyal Extreme – 1% Hyaluronic Acid in double molecular weight (HMW and MMW) combined with antioxidant and soothing actives such as Vitamin E. Formulated with Glycerosomal technology – Prigen patent – which implements the product’s performance up to 5 times.
Gen-Hyal EYES – 2% Hyaluronic Acid in double molecular weight (HMW and MMW) combined with draining and flaming active ingredients such as caffeine and centella asiatica (puffiness and dark circles), aloe (soothing) and vitamin E (antioxidant). Formulated with Glycerosomal technology – patented by Prigen – which implements the product’s performance up to 5 times.
Gen-Hyal URBAN SERUM – Hyaluronic Acid 0.75% high molecular weight (HMW) combined with antioxidant and soothing (vitamin E), regenerative (Tetraselmis Suecica) and detoxifying (Moringa Oleifera) active ingredients. Formulated with Glycosomal technology – patented by Prigen – which implements the product’s performance up to 5 times.
Gen-Hyal Anti-age UV SHIELD with spf 30+ UVB / UVA – 0.5 % high molecular weight Hyaluronic Acid (HMW) combined with regenerative (Tetraselmis Suecica), detoxifying (Moringa Oleifera) and chemical filters for daily summer/winter protection against UVA and UVB rays. It is not a sunscreen but a daily anti-ageing serum.
Gen-Hyal Bioactive LIP CARE – lip balm with 0.02% Hyaluronic Acid. In this lip balm the Hyaluronic Acid is contained at the highest possible percentage given the very small percentage of water. The product in fact has a compact and buttery form, due to the mix of vegetable oils such as avocado, olive, jojoba and sunflower to soften the lips, nourish them and make them more elastic. It also contains Vitamin E and Tetraselmis Suecica to bring immediate relief to dry lips by counteracting natural oxidative stress.
Small note on cosmetic label information
Gen-Hyal products are developed with very high concentrations of Sodium Hyaluronate compared to most brands on the market.
When we talk about the concentration of Sodium Hyaluronate in a cosmetic we mean the percentage of this powder dissolved in water. For example, if we consider 0.5% Sodium Hyaluronate in a 100 ml bottle, we mean that 99.5% is water and the remaining 0.5% Sodium Hyaluronate, i.e. 99.5ml water + 0.5g Sodium Hyaluronate.
When using a high molecular weight Sodium Hyaluronate, for example, it is untrue to assume that a concentration of more than 3% is used because, due to its high viscosity, an almost inhalable gel would be obtained. Above this threshold, in fact, the formulation results in a gel that is so viscous that if placed in a glass and turned upside down it will tend to stick to the bottom of the glass, thus rendering it practically unusable for cosmetic purposes. In the Prigen laboratories we have therefore identified in the 2% double molecular weight (Gen-Hyal Premium and Gen-Hyal Eyes) the best compromise between % Sodium Hyaluronate and spreadability of the product.
Any indication on the label that states percentages of 40%-50% Sodium Hyaluronate (especially if they specify high molecular weight) is to be considered a mere communication ploy. In reporting such high percentages, the reference is not to the actual concentration of Sodium Hyaluronate present in the bottle, but to the quantity (expressed as a percentage) that is used in a much more diluted starting solution, which is then further diluted to 100%.