"There are several different groupings of hyaluronic acid fillers, but they are not as different as the numerous brand names may suggest. The state-of-the-art engineering techniques currently used in the production of modern fillers has resulted in safer products, regardless of the specific origin of the HA contained in the filler product," says Tanja C. Fischer, M.D., a dermatologist at the Skin and Laser Center, Potsdam, Germany.
ANIMAL VERSUS NOT The main difference among HA fillers in regards to their source are animal-derived and non-animal-derived (non-animal-derived synthetic hyaluronic acid, NASHA). The animal-derived HA fillers have become less popular over the years, in part due to the concern of an allergic reaction to the foreign proteins contained in the filler and the potential risk of disease transfer, as well as for the subsequent development of foreign-body granulomas, coupled by promotional spins from the NASHA manufacturers."The animal-derived HA fillers are never 100 percent 'pure' and could potentially cause complications, as the proteins and DNA they contain are species-specific. However, in practice, this is not a major source for concern with modern animal-derived HA fillers. Nevertheless, the companies who manufacture the NASHA products spend a great deal of resources convincing consumers to stay away from animal-derived HAs and buy into so-called 'riskless' non-animal derived HAs," says Eckart Haneke, M.D., professor, department of dermatology, University of Berne, Switzerland.
OTHER FEATURES HA filler products can be further subdivided into mono-phasic and biphasic as well as non-cross-linked and cross-linked. According to Dr. Haneke, the cross-linked HAs are the most popular, representing approximately 99 percent of all currently available fillers. Their popularity is directly due to their heightened ability to resist enzymatic degradation, which in practice translates into an extended longevity of cosmetic effect, he says.
"Natural HA is degraded and resynthesized within the span of a few days. Cross-linked HAs are more resistant and therefore remain longer in the tissue. One of the biggest advantages with HA is that if you over-correct or have a less-than-optimal cosmetic outcome, you can dissolve the product with hyaluronidase within a few hours, regardless of the source, degree of cross-linking, or chemical used for that cross-linking," Dr. Haneke says.
HAs are also further differentiated and classified according to their molecular weight. Perlane (Medicis) and Restylane (Medicis) may be considered optimal for the treatment of fine lines and rhytids due to their small molecular size, compared to Macrolane (Q-Med), which has a much larger molecule and could be ideal for deeper filling and volume replacement, Dr. Haneke says.
"If the molecules in the filler are too small and you inject too deep in the tissues, the cosmetic effect will be less, and if they are too big and you inject too superficially, you may get palpable lumps and bumps in the skin. Therefore, choosing an optimal size molecule in respect to the cosmetic correction to be made is crucial," Dr. Fischer says.
In the hopes of differentiating themselves further from their competitors, several manufacturers are adding lidocaine to their HA filler products, such as Juvéderm Ultra (Allergan).