Simply put, hyaluronic acid (HA) is a substance composed of a long chain of sugar molecules strung together like a necklace. It is naturally found throughout our bodies, where it acts as a binding, lubricating, and protective agent.^8-12.

What is hyaluronic acid made up of? 

Hyaluronic acid belongs to a group of naturally occurring organic compounds called glycosaminoglycans: essentially, a very long chain of two repeating simple sugars (N-Acetylglucosamine and glucuronic acid) that are linked together to form what is scientifically known as a disaccharide unit (see Figure). The number of repeat disaccharide units per chain is between 2 500 - 25 000.^8,12,13,15

Hyaluronic Acide structure¹⁶ 

HA structural roles

Hyaluronic acid is one of the main elements of the extracellular matrix (ECM): this matrix creates spaces between cells and acts as a scaffold to all living cells and determines how our tissues look and function. Other major components of the ECM are collagen and elastin. ^11,12,17
 

Components of the ECM and their roles¹⁷

The molecular structure and large size of Hyaluronic Acid give it exceptional water binding capacity and high viscosity, both important characteristics of injectable and skincare products.^12,18-20

Size really does matter

The difference in size (molecular weight) of HA determines its functions and uses.^13,21-23

• High molecular weight (HMW-HA) has the ability to trap large amounts of water, and therefore serves to lubricate, hydrate, or space-fill tissues such as joints and connective tissue. It also plays a role in the organisation of the ECM.^12,11,13
• Low molecular weight HA (LMW-HA) acts as a “danger signal” and provokes inflammation; something that should be avoided as it ultimately destroys our collagen and elastin.^_2,11,13,21

Biological roles

Hyaluronic acid plays a critical role in skin health by stimulating the production of cells called fibroblasts, which in turn are responsible for producing collagen and elastin.²⁴ Hyaluronic Acid thus provides our skin with the desired hydration and elasticity while keeping our skin firm and supple.¹⁷

Hyaluronic acid also acts as an antioxidant: it protect our cells, such as fibroblasts mentioned above, and therefore allows the ECM to function correctly (for example, in wound healing).^5,22,25

The vicious circle of skin ageing ^22,25,26,42

In a nutshell…

Hyaluronic acid is a natural product. It is found throughout our bodies and is necessary for it to function properly ²². HA is found in our skin, inside our joints, within our eyes and in other tissues where it helps improve collagen production, increase moisture levels in the skin, provide elasticity and flexibility, and accelerate skin regeneration and healing.

Hyaluronic acid is most abundant in our skin, accounting for almost 50% of the total HA in our bodies.¹² It is found mainly in the deep, underlying area of our skin (dermis) but also in the outermost visible layer (epidermis). However, in the epidermis, HA is short-lived and only lasts 2-3 hours before it is destroyed.^11,12,22

With this in mind and knowing that Hyaluronic Acid is non-toxic, non-irritating and non-allergenic due to its natural presence in the skin, HA is undoubtedly an attractive ingredient in skincare products.⁵

When high molecular weight HA (HMW-HA) is injected into the dermis of our skin, it promotes skin rejuvenation by increasing both hydration and fibroblast activation.²⁶ It can also plump up wrinkles: in this case, the injected Hyaluronic Acid is more commonly known as a dermal filler which slowly degrades over the course of months to produce long lasting results.^27,31

• Since HA is rapidly degraded in the skin, cross-linking HA, in dermal fillers provides increased stability and can enhance its mechanical characteristics.^12,22,27,28
  • Moreover, facial dynamics can be better respected nowadays by using innovative cross-linking methods. These methods allow dermal fillers o better represent the natural hyaluronic acid found in our bodies, even after the cross-linking and modification process.²⁹

When used in cosmetics, Cross-linked HMW-HA is used as a moisturiser because it is not absorbed once applied to the skin.⁵ Instead, it creates an invisible barrier on our skin’s surface that holds in moisture and helps to preserve the principal characteristics of young healthy skin: smoothness, elasticity, and tone, which can reduce the look of fine lines and wrinkles.²⁸

This has been verified in a study showing that crosslinked HMW-HA in cosmeceuticals also provides better results on skin quality compared to non-crosslinked HMW and LMW HA.²⁸

Products containing Hyaluronic Acid can be found in various formulations and are registered as medicines, medical devices or cosmetic products.⁵

Hyaluronic acid is widely used as an active ingredient in many beauty products. ^5,32

• Injectable HA gels, are used to reduce wrinkles in dynamic and static zones and can help to model cheeks, to correct facial lines and the shape of lips and to improve elasticity and hydration of facial, hand, neck and neckline skin.
• Creams and serums, whereby crosslinked-HA it functions as a protective barrier on the skin to maintain moisture, thus giving our skin a more hydrated appearance.
• Cleansing solutions to improve our skin’s elasticity and hydration before applying makeup.
• Make-up foundations, resulting in a complexion that stays hydrated all day long whilst protecting from environmental-related skin ageing.