Long-lasting and permanent fillers: biomaterial influence over host tissue response.

BACKGROUND: The purpose of this study was to attempt to understand why some injectable fillers produce frequent ill effects and some do not, by reviewing the available agents and analyzing them through the knowledge of biomaterial studies, which show clearly what type of reactions can be expected according to the chemical used.
METHODS: A study of long-lasting and permanent fillers was performed in an attempt to understand the specific reactions induced by each agent. Agents were then compared with manufacturers' allegations and published data on complications.
RESULTS: All the available products have a potential for complications. However, the difference between the normal healing process and true inflammatory granuloma must be established. For a volume effect, the implant, although deep, should induce the smallest inflammatory reaction, to avoid any long-term side effects. Particulate implants with porous or irregular surfaces are potentially more reactive than spherical, smooth-surface particles. Gels and oils have a potential for fragmentation, and each droplet will start a new inflammatory phase. For a superficial treatment, is seems better to use a "passive" filler, which should have no inflammatory reaction. The problem remains for combined indications: volume and smoothing, deep and superficial. After hyaluronic acid injections in areas previously treated with a nonresorbable agent, severe inflammatory granulomas have appeared, and it is not possible to state whether they are attributable to the new product, even a resorbable one, or to reactivation of the sleeping reaction from the previous implant.
CONCLUSION: There is an obvious need for serious, precise, and objective studies on most of the available fillers, which have not been properly scientifically studied on human skin.