Hyaluronic acid is a naturally-occurring molecule found in the human body especially in skin, joints, and nerves. HA is found in relatively high concentrations in the basal layer of the epidermis where proliferating keratinocytes are found. It functions as a cushion and lubricant with the ability to hold up to 1,800 times its own weight in water due to its chemical structure. The primary structure of hyaluronic acid consists of a repetitive disaccharide unit, of sodium glucuronate and N-acetyl glucosamine bound by a β (1-3) bond. These units are linked with a β (1-4) bond. In solution, because of the number of anionic residues on its surface, HA is able to attach to many free water molecules. Polymers of hyaluronic acid can range in various sizes of molecular weight from 5,000 Daltons to 20,000,000.

Molecular Formula: C28H44N2NaO23+Molecular Weight: 799.641 g/mol

Sodium hyaluronate is the sodium salt of hyaluronic acid. Similar to hyaluronic acid, sodium hyaluronate can range in various sizes of molecular weight. However, as a rule of thumb, sodium hyaluronate tends to be available on the lower range of molecular sizes and therefore is generally regarded as less desirable.

Uses and Benefits

Hyaluronic acid (HA) and sodium hyaluronate come in varying sizes. High-molecular weight HA is longer polymer chains whereas low-molecular-weight HA can penetrate the skin deeper. The high-molecular form of HA has a better hydrating effect than the low-molecular form of HA as it remains on the skin outer surface to retain water moisture and form a protective layer. High-molecular form of HA moisturizes the skin by preserving the skin’s water content and results in skin softness and reduced appearance of skin dryness. It is used as a humectant to increase moisture in the skin. Many products may contain HA or sodium HA and the efficacy of this ingredient will depend on the molecular weight used and its purity.

Safety

Hyaluronic acid (HA) and sodium hyaluronate is naturally occurring in our bodies and is safe. The Environmental Working Group rates hyaluronic acid on a scale of 1 to 10 (where 1 is safe and 10 is a high safety risk) as a 1.

References

Ammi R, Ripellino JA, Margolis RU, Maibach HI, Tammi M (1989). "Hyaluronate accumulation in human epidermis treated with retinoic acid in skin organ culture". J. Invest. Dermatol. 92 (3): 326–32.