[4] Medically, hyaluronic acid is used to treat osteoarthritis of the knee and dry eye, for wound repair, and as a cosmetic filler.

[5] The average 70 kg (150 lb) person has roughly 15 grams of hyaluronan in the body, one third of which is turned over (i.e., degraded and synthesized) per day.

[6] As one of the chief components of the extracellular matrix, it contributes significantly to cell proliferation and migration, and is involved in the progression of many malignant tumors.

[10][11][12] Until the late 1970s, hyaluronic acid was described as a "goo" molecule, a ubiquitous carbohydrate polymer that is part of the extracellular matrix.

[citation needed] Hyaluronic acid is an important component of articular cartilage, where it is present as a coat around each cell (chondrocyte).

When aggrecan monomers bind to hyaluronan in the presence of HAPLN1 (hyaluronic acid and proteoglycan link protein 1), large, highly negatively charged aggregates form.

A particular type of fibroblasts, embedded in dense fascial tissues, has been proposed as being cells specialized for the biosynthesis of the hyaluronan-rich matrix.

When skin is exposed to excessive UVB rays, it becomes inflamed (sunburn), and the cells in the dermis stop producing as much hyaluronan and increase the rate of its degradation.

[18] As a major component of the extracellular matrix, hyaluronic acid has a key role in tissue regeneration, inflammation response, and angiogenesis, which are phases of wound repair.

[19][20] There is also some limited evidence to suggest that hyaluronic acid may be beneficial for ulcer healing and may help to a small degree with pain control.

Initiation of inflammation is crucial for the formation of granulation tissue; therefore, the pro-inflammatory role of HA as discussed above also contributes to this stage of wound healing.

[23] CD44 is collocated with HA in the basal layer of epidermis where additionally it has been shown to be preferentially expressed on plasma membrane facing the HA-rich matrix pouches.

[24] Maintaining the extracellular space and providing an open, as well as hydrated, structure for the passage of nutrients are the main functions of HA in epidermis.

[25] A 2012 review showed that the quality of studies supporting this use was mostly poor, with a general absence of significant benefits, and that intra-articular injection of HA could possibly cause adverse effects.

[26] A 2020 meta-analysis found that intra-articular injection of high molecular weight HA improved both pain and function in people with knee osteoarthritis.

[38] Hyaluronic acid is produced on a large scale by extraction from animal tissues, such as chicken comb, and from Streptococci.

[41] Hyaluronic acid is synthesized by a class of integral membrane proteins called hyaluronan synthases, of which vertebrates have three types: HAS1, HAS2, and HAS3.

These enzymes lengthen hyaluronan by repeatedly adding D-glucuronic acid and N-acetyl-D-glucosamine to the nascent polysaccharide as it is extruded via ABC-transporter through the cell membrane into the extracellular space.

[47] Bacillus subtilis recently has been genetically modified to culture a proprietary formula to yield hyaluronans,[48] in a patented process producing human-grade product.

A fasciacyte is a type of biological cell that produces hyaluronan-rich extracellular matrix and modulates the gliding of muscle fasciae.

[43] Hyaluronic acid (HA) is a linear glycosaminoglycan (GAG), an anionic, gel-like, polymer, found in the extracellular matrix of epithelial and connective tissues of vertebrates.

[51] In addition, recent studies showed hyaluronan fragments, not the native high-molecular weight molecule, can induce inflammatory responses in macrophages and dendritic cells in tissue injury and in skin transplant.

Hyaluronic acid was first obtained by Karl Meyer and John Palmer in 1934 from the vitreous body in a cow's eye.

[58] Native hyaluronic acid has a relatively short half-life (shown in rabbits)[59] so various manufacturing techniques have been deployed to extend the length of the chain and stabilise the molecule for its use in medical applications.

[63] In the late 1970s, intraocular lens implantation was often followed by severe corneal edema, due to endothelial cell damage during the surgery.

[70] Due to its accumulation in airway epithelial cells in various respiratory diseases, such as COVID-19, cystic fibrosis, influenza, and sepsis, hyaluronic acid is under study as a possible mediator of lung inflammatory mechanisms, as of 2022.

[72] In particular, research groups have found hyaluronan's properties for tissue engineering and regenerative medicine may be improved with cross-linking, producing a hydrogel.

[78] Due to its ability to regulate angiogenesis by stimulating endothelial cells to proliferate in vitro, hyaluronan can be used to create hydrogels to study vascular morphogenesis.