ABSTRACT
Injectable filling agents are most commonly classified according to their duration within the human tissues, as short-or moderate-lasting agents: 3-12 months, or long-lasting or permanent fillers, whose duration is at least 12-18 months. However, they can also be considered according to
the reactions they induce within human tissues. Any implantation of a device into the human body starts a reaction of identification, isolation from the host tissues, and, if recognized as dangerous, its removal. This is the foreign body reaction.
