It is noteworthy that the maturation and aging of human skin is accompanied by considerable alterations in HA content and metabolism. Aging of the skin is also associated to the deterioration of the mechanical and viscoelastic properties of the intercellular matrix. This infers that the presence of a hydrated viscoelastic HA network in the intercellular matrix is vital to maintain a healthy young skin. Several studies reported in the "Journal of Dermatology" have revealed that HA levels were reduced in the parts of the patient's skin where signs of premature aging have appeared while HA levels were normal on other parts of the skin of the same patient.7,8,12

Hyaluronan (hyaluronic acid) derivatives such as hylan gels are well suited for use in dermal augmentation due to their insolubility and resistance to degradation. Their high water content, viscoelastic properties (similar to native HA) and ability to mimic the natural hydrating functions of HA together with the fact that hylan gel implants do not elicit inflammatory, immunologic (cellular or humoral) or foreign body reactions, contribute to their stability and compatibility with human tissue. 8,12

Hylan gels serve as scaffolding in directing and controlling tissue regeneration and as space-fillers for the tissue. While Hylan gels are proven to operate in a similar manner to native HA polymer in these functions, other materials do not present the same properties as HA. For instance, Collagen implants are known to resorb, elicit an inflammatory reaction and a granulocyte response that is followed by infiltration of macrophages. PMMA (polymethyl methacrylate), paraffin, silicone and Teflon often elicit intense foreign body and other reactions; in addition, they have a tendency to migrate from the site of injection, they are no longer in frequent use.9,12