Hyaluronic acid, also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues.

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. Hyaluronic acid is a major component of skin, where it is involved in repairing tissue. 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. Hyaluronan degradation products then accumulate in the skin after UV exposure.

Hyaluronic acid has been FDA-approved to treat osteoarthritis of the knee via intra-articular injection. Dry, scaly skin, such as that caused by atopic dermatitis, may be treated with lotion or another skin product containing sodium hyaluronate as its active ingredient. Hyaluronic acid has been used in various formulations to create artificial tears to treat dry eye.

Hyaluronic acid is a common ingredient in skin care products. Hyaluronic acid is used as a dermal filler in cosmetic surgery.

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