Hyaluronic Acid: Skin Benefits, Molecular Weights and Types

Hyaluronic acid is one of the most popular hydrating ingredients in skincare. This essential molecule is a polysaccharide that is capable of holding up to a thousand times its weight in water. Hyaluronic acid is naturally occurring in the skin and the fluids around the body’s joints, the stomach, and the eyes. In the body it is used for healing wounds, calming inflammation, and tissue repair. As we age and we are exposed to factors, such as UV radiation and pollution, the levels of hyaluronic acid in our body significantly decrease. This contributes to the appearance of dryness, fine lines and wrinkles, loss of firmness, and uneven skin texture.

Benefits of Using Hyaluronic Acid
Hyaluronic acid in cosmetic formulations is a powerful humectant that attracts and retains water from its surroundings. Applied topically, it is an excellent moisturiser that delivers smooth, plump and luminous look to the skin. It is often used in serums and creams to improve skin’s elasticity and hydration.
As a natural component in skin, hyaluronic acid has little to no side effects and is safe for all skin types, including sensitive and atopic skin.

Difference Between Topical and Injectable Hyaluronic Acid
Delivered topically, hyaluronic acid is a large molecule that cannot fully penetrate the skin for significant results, so it primarily works as a humectant on the surface. However, lower molecular sizes can reach deeper into the epidermis. Visible improvement in skin’s hydration and firmness can be attained within a few weeks and therefore, consistency is key.
Hyaluronic acid injections, also known as dermal fillers, absorb water and fill areas to temporarily increase the volume of the skin. The effect can be noticed immediately and lasts between 3 to 12 months before hyaluronic acid is gradually absorbed by the body.

Hyaluronic Acid Molecular Weights
The size of hyaluronic acid molecules varies from larger molecules that remain closer to the skin’s surface to smaller ones that can penetrate deeper into the epidermis and sustain the skin’s moisture content. To deliver optimal results, a serum or a cream formulation usually contains a combination of molecular weights.
The different molecular sizes are indicated by unified atomic mass units, called Daltons (kDa).

We can distinguish several hyaluronic acid (HA) molecular sizes:
• High molecular HA (>1000 kDa) – it cannot penetrate the skin barrier, however, it has anti-inflammatory properties, improves skin’s elasticity and creates a moisturising layer on the surface of the skin.
• Medium molecular weight HA (250-1000 kDa) – promotes skin elasticity and firmness, and helps prevent dehydration.
• Low molecular weight HA (10-250 kDa) – it has longer-lasting effects, carries wrinkle-smoothing properties, and keeps the moisture in the skin.
• Oligo-HA (<10 kDa) – an ultra-low molecular weight hyaluronic acid that has regenerating properties and penetrates deeper into the skin. It has long-lasting effects, visibly reduces fine lines and wrinkles and makes the skin appear smoother and firmer.

Types of Hyaluronic Acid
There are three types of hyaluronic acid that are most commonly found in skincare:
• Hydrolysed hyaluronic acid – a way to minimise the large hyaluronic acid molecule is by breaking it down via a chemical reaction with water (hydrolysing). This way it penetrates the skin better and attracts significant amounts of water to leave the skin hydrated and plump.
• Sodium acetylated hyaluronate – a hyaluronic acid derivative, synthesised from sodium hyaluronate by acetylation reaction. It has higher water-binding ability, repairs skin barrier function, and reduces water evaporation from the skin.
• Sodium hyaluronate – a salt derived from hyaluronic acid that can penetrate into deeper layers of the skin to improve skin’s elasticity, reduce the signs of ageing, and protect from environmental aggressors.

In cosmetic formulations high molecular hyaluronic acid thickens the water phase and increases the viscosity, turning it into a gel. That is why only a small amount between 0.1% - 0.3% can be used and it creates a moisturising film on the surface of the skin. Lower molecular hyaluronic acid can be used in higher concentrations of up to 2% and it can penetrate deeper into the skin for visible results.