Hyaluronic acid (also called Hyaluronan or hyaluronate) is a non-sulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is one of the chief components of the extracellular matrix, contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumors. The average 70-kg man has roughly 15 grams of hyaluronan in his body, one-third of which is turned over (degraded and synthesised) every day.

Medical applications
Hyaluronan is naturally found in many tissues of the body, such as skin, cartilage, and the vitreous humor. It is therefore well suited to biomedical applications targeting these tissues. The first hyaluronan biomedical product, Healon, was developed in the 1970s and 1980s by Pharmacia, and is approved for use in eye surgery (i.e., corneal transplantation, cataract surgery, glaucoma surgery and surgery to repair retinal detachment). Other biomedical companies also produce brands of hyaluronan for ophthalmic surgery.

Hyaluronan is also used to treat osteoarthritis of the knee.Such treatments, called viscosupplementation, are administered as a course of injections into the knee joint and are believed to supplement the viscosity of the joint fluid, thereby lubricating the joint, cushioning the joint, and producing an analgesic effect. It has also been suggested that hyaluronan has positive biochemical effects on cartilage cells. However, some placebo controlled studies have cast doubt on the efficacy of hyaluronan injections, and hyaluronan is recommended primarily as a last alternative to surgery. Oral use of hyaluronan has been lately suggested, although its effectiveness needs to be demonstrated. At present, there are some preliminary clinical studies that suggest that oral administration of Hyaluronan has a positive effect on osteoarthritis, but it remains to be seen if there is any real benefit to the treatment.

Due to its high biocompatibility and its common presence in the extracellular matrix of tissues, hyaluronan is gaining popularity as a biomaterial scaffold in tissue engineering research.

In some cancers, hyaluronan levels correlate well with malignancy and poor prognosis. Hyaluronan is thus often used as a tumor marker for prostate and breast cancer. It may also be used to monitor the progression of the disease.

Hyaluronan may also be used postoperatively to induce tissue healing, notably after cataract surgery. Current models of wound healing propose that larger polymers of hyaluronic acid appear in the early stages of healing to physically make room for white blood cells, which mediate the immune response.

Hyaluronan has also been used in the synthesis of biological scaffolds for wound healing applications. These scaffolds typically have proteins such as fibronectin attached to the hyaluronan to facilitate cell migration into the wound. This is particularly important for individuals with diabetes who suffer from chronic wounds.

In 2007, the EMEA extended its approval of Hylan GF-20 as a treatment for ankle and shoulder osteoarthritis pain.

Cosmetic applications
Hyaluronan is a common ingredient in skin care products.

In 2003 the FDA approved hyaluronan injections for filling soft tissue defects such as facial wrinkles. Restylane is a common trade name for the product. Hyaluronan injections temporarily smooth wrinkles by adding volume under the skin, with effects typically lasting for six months. People who have been on any blood medication with in the last five years should not inject this drug until the five year span is over. It is alleged that this drug is not suitable for use in elderly patients because it can cause memory loss, although there is no evidence in the literature of any negative cognitive effects attributable to hyaluronic acid injections.