Introduction

Hyaluronic acid (synonym: Hyaluronan, HA) is an important component of the human skin. It is synthesized with the help of the enzyme hyaluronate synthase (HAS) by fibroblasts of the dermis and epidermis. As the main component of the extracellular matrix it also occurs in other types of the human connective tissue.
Chemically speaking, hyaluronic acid (HA) is a glycosaminoglycan (Fig. 1). Its basic structure is a disaccharide of about 400 Dalton which is composed of D-glucuronic acid and N-acetylglucosamine linked together through alternating beta-1,4- and beta-1,3 glycosylic bonds. The specific basic structure and high packing densities are responsible for the fact that HA has a gel-like consistency in water.