What it is
Hyaluronic acid is an anionic, nonsulfated glycosaminoglycan made of repeating disaccharide units of D-glucuronic acid and N-acetyl-D-glucosamine, forming very long chains. It is a natural component of skin, where it helps maintain hydration. In cosmetics it acts like a sponge that binds water, and its behavior depends on molecular weight: high-molecular-weight hyaluronic acid stays on the surface to give immediate hydration and a protective film, while lower-molecular-weight forms work somewhat deeper, mainly within the epidermis. In sunscreens it is included as a hydrating, conditioning ingredient and is not a UV filter.
Safety & warnings
As a skin-identical humectant, ordinary hyaluronic acid is widely used and well tolerated. Ingredient references note that standard low-molecular-weight hyaluronic acid appears safe, while cautioning about ultra-low-molecular-weight versions below about 50 kDa, since one study found a roughly 20 kDa fragment showed some pro-inflammatory activity. For typical cosmetic-grade material this is a niche concern; reactive skin types can patch test new products.
Origin & sourcing
Hyaluronic acid is naturally present in skin and connective tissue. For cosmetic use it can be extracted from animal sources such as rooster comb, but the preferred modern method is bacterial fermentation, including the use of genetically modified Bacillus subtilis to produce hyaluronans without animal-derived material.
History
Hyaluronic acid was first obtained by Karl Meyer and John Palmer in 1934 from the vitreous body of a cow's eye, which is how the compound was originally isolated and named.
Questions everyone asks
Does hyaluronic acid offer sun protection?
No. It is not a UV filter. In sunscreens it is there to hydrate and condition skin, while the UV filters provide protection.
Does molecular weight matter?
Yes. High-molecular-weight hyaluronic acid hydrates and films the surface, while lower-molecular-weight forms work somewhat deeper, mainly in the epidermis.
Is it vegan?
It can be. While it can be sourced from rooster comb, most modern cosmetic hyaluronic acid is made by bacterial fermentation, which avoids animal-derived material.