Hyaluronic Acid

Hyaluronic acid, also called hyaluronan, is a glycosaminoglycan: a long chain of sugar units found in the skin and other tissues of vertebrates. It can bind large amounts of water. In cosmetics, it and its salts are used as skin- and hair-conditioning agents and humectants.

Structure and properties

The chain is linear and made of repeating two-sugar units of glucuronic acid and N-acetylglucosamine. Hyaluronic acid dissolves in water and has a high capacity for water retention: 1 g can hold up to 6 litres of water. In water, its coiled chains trap water and form a network with each other. Such solutions are viscous, and the viscosity rises with concentration and chain length. The molecular weight of hyaluronic acid used in cosmetics ranges widely, from 5 to 1,800 kDa, depending on how it is made.

In the body

Hyaluronic acid occurs throughout vertebrate tissues, for example in the brain, the vitreous humour of the eye and the skin. In human skin it is the most abundant glycosaminoglycan and helps keep the tissue hydrated. It is renewed quickly: its half-life in the skin is about one day.

Forms and production

For cosmetic use, hyaluronic acid is made by bacterial fermentation or extracted from rooster combs. Both sources give exactly the same structure. The most common name on cosmetic ingredient lists is by far sodium hyaluronate, the sodium salt. Hydrolysed hyaluronic acid has shorter chains, cut chemically or by enzymes.

Use in cosmetics

The EU cosmetic ingredient database (CosIng) lists sodium hyaluronate as a humectant and skin-conditioning ingredient. In 2023, sodium hyaluronate was reported to the US Food and Drug Administration as used in 4,713 cosmetic formulations, at up to 7.5% in face and neck products. How far it enters the skin depends on chain size: molecules below 400 kDa can at least spread within the outermost skin layer, the stratum corneum. In a test on human skin samples, most of the applied hyaluronic acid stayed in the stratum corneum, whatever its size.

Safety

In 2023 the Cosmetic Ingredient Review (CIR) expert panel found hyaluronic acid and six related ingredients safe as then used in cosmetics. Some of the material comes from rooster combs. The panel therefore stressed that manufacturers should keep limiting infectious agents and biological impurities, such as nucleic acids, proteins and endotoxins.

Products containing it

• Anti-Aging Face Cream With Lavender (I 885)
• Eye Contour Cream, Secret Of Serenity (I 406)
• Face Cream For Night Use, Secret Of Serenity (I 401)
• Face Cream, Argana (I 897)
• Shampoo With Calendula (I 778)
• Shampoo With Dead Sea Salt, Viva Activ (I 779)
• Skin Cream With Dead Sea Salt, Viva Activ (I 877)