Hyaluronic acid is a mucopolysaccharide that is part of a family called the glycosaminoglycans. These long-chain sugar molecules appear naturally in cell membranes throughout the human body, and help with hydration of tissues and other important cell functions. For supplementation, hyaluronic acid may be produced using animal sources, but can also be isolated from fermented bacteria.^[4]

HA is useful in several branches of medicine. Ophthalmologists use it in the treatment of dry eye syndrome,^[2] orthopedics specialists use it for different types of arthritis and joint pain,^[5][6][7] and aesthetic practitioners use HA in fillers.^[8] It seems to have potential in other areas, too, such as wound healing and the treatment of burns.^[9][10] In all of these applications, HA helps with hydration, lubrication, and tissue regeneration. High-molecular-weight HA is produced in healthy cells. Molecular weight is measured in daltons, which is the unit used to express the weight of atoms and larger molecules. A high molecular weight for HA is above 2000 kilodaltons (kDa). High-molecular-weight HA is associated with anti-inflammatory effects, and seems to slow down immune responses.^[11] Other potential uses that are being looked into include alopecia treatments, regeneration of nerves in peripheral neuropathy, and use of HA in vascular grafts to help with healing.^[12][13]

Since hyaluronic acid is found within the body and is naturally produced in the cell membranes, it is biocompatible and rarely causes any adverse effects. In products made from animal sources, the potential for an allergic reaction exists, but is unlikely.^[10][4]

One potential drawback of endogenous HA is that cancer cells may also produce high-molecular-weight HA. In these cells, the regenerative properties of HA support tumor growth by improving blood supply and can even protect the tumor from anticancer drugs. Some cancer treatments therefore include hyaluronidase to break down HA so that the medication can reach the tumor.^[4] At very low molecular weights, measured as 40 KDa and below, HA can be a sign of stress and may be associated with inflammation.^[10]

HA is a large hydrophilic molecule. When it is released from cells, it binds water, and this helps with hydration of the cells. It also attracts fluid into the synovial fluid of the joints and the vitreous fluid in the eye, hydrating and lubricating these areas. When it is produced by cells, HA is a long molecule with a high molecular weight. In this form, it binds to certain proteins produced by the immune system, such as IL-8, and prevents autoimmune responses and inflammation.^[10]