Does hyaluronic acid dry out the skin?

Beware, it is common to read that hyaluronic acid can dry out the skin. According to some beliefs that are not scientifically proven, hyaluronic acid would draw the water it needs from the skin's reserves if the surrounding air is too dry, which would dry out the epidermis. However, the reality is quite the opposite! Hyaluronic acid-based actives hydrate the skin, to varying depths depending on their molecular weight.

Reminders about Hyaluronic Acid

Hyaluronic acid (HA) is a complex sugar extremely hydrophilic, naturally present in the human body in the joints, muscles, eyes and especially the skin.Nearly 50% of its total quantity is housed in the dermis, the deep layer of the skin. It constitutes the extracellular matrix and serves as a support to collagen and elastin fibres. It also ensures skin hydration as it acts like a molecular sponge: it captures water molecules and retains them.

Epidermal and dermal cells are capable of synthesising HA. The dermis, being much thicker than the epidermis, contains four to nine times more HA. However, it has been demonstrated that, for an equivalent amount of tissue, the epidermis synthesises four times more hyaluronic acid than the dermis.

Skin cells lose their ability to produce optimal quantities of Hyaluronic Acid (HA) during the ageing process. This is why baby skin is so soft and smooth: it is rich in HA. However, as we age, dehydration occurs; the skin thins and wrinkles appear. The decline in HA production also results in a decrease in suppleness, a reduction in elasticity, and a loss of skin tone. In aged skin, HA is still present in the dermis, while the HA in the epidermis has completely disappeared.

Today, the reasons for the precipitous drop in HA with ageing are unknown. In order to combat this phenomenon, it is recommended to continue "recharging" the skin with HA from adolescence. It is already known that orally ingested HA presents no benefits for the skin, as skin cells are incapable of extracting HA from the bloodstream. The "recharging" of the skin with HA is more reliably achieved through the topical application of HA-rich skincare products.

The various molecular weights of hyaluronic acid

The process of skin hydration operates according to a highly complex mechanism. Depending on the molecular weight of hyaluronic acid, it will have different effects on skin hydration. The higher the molecular weight of the hyaluronic acid, the more dominant the physico-chemical properties become, while the biological properties will prevail in the case of low molecular weight fragments.

• Thehigh molecular weight hyaluronic acid (>1,800kDa)helps to increase the viscosity of a formula and forms a viscoelastic film when applied to the skin. Thus, high molecular weight hyaluronic acid has a positive effect on the hydration of the upper layers of the epidermis, which is manifested by a decrease in trans-epidermal water loss due to its occlusive action. Moreover, this film-forming effect enhances the penetration of other active ingredients present in the formula.

• Thelow molecular weight hyaluronic acid (> 100-1000 kDa)allows for deeper skin hydration due to its profound penetration. It interacts with skin cells and components of the extracellular matrix. It is effective in improving skin texture and reducing wrinkles.

• The very small hyaluronic acid fragments (50 kDa and less) are highly beneficial in combating ageing because, after penetrating the deeper layers of the skin, they act as signalling molecules for the epidermal cells to synthesise new endogenous high molecular weight hyaluronic acid molecules, which has a positive effect on overall hydration. Furthermore, the hyaluronic acid fragments reduce the creation of pro-inflammatory interleukins, responsible for generating free radicals capable of damaging the components of the extracellular matrix and the skin cells themselves.