Juvederm is derived from a bacterial source, streptococcus equi. Don't worry this is a harmless bacteria species to start off with. It is then broken down so the hyaluronic acid part is extracted out. (Back in 1965, I was extracting lipopolysaccharides from E. Coli a truly dangerous bacteria, but the extract was harmless....though we never thought of injecting it into people!). This bacteria-derived hyaluronic acid is also a polysaccharide, a glorified sugar molecule. Since hyaluronic acid has no tissue specific or species specific antigens (proteins that can cause a reaction) it is thought to be virtually impossible to develop an allergic reaction to Juvederm, Restylane, Captique or Hylaform. The latter isderived from rooster combs, and while it too has little tendency for an allergic reaction it seems to have fallen out of favor. Each of the hyaluronic acid fillers have different chemical properties depending not on the molecule itself but on the method used when it was extracted. The difference in qualities include: gel hardness, flow, particle size, concentration of particles in the gel (this say separates Perlane from Restylane and Juvederm Ultra from Juvderm Ultra Plus... Perlane and Juvederm Ultra Plus having more particles), swelling or the resistance to dilution...this accounts for the difference in longevity between the products; solubility, and finally cross-linking. The Allergan people boast about the Hylacross technology of their product, Juvederm, which allows more cross-linking and smoothness. Hopefully, this answers your excellent question.