An allergic reaction to a Radiesse injection does not occur because it is not a reactive substance and is truly biocompatible. There are, however, possible side effects that can occur. These side effects include swelling, bruising, mild irritation and redness (that may look like an allergic reaction), and tenderness. Rarely, if the Radiesse is injected into a blood vessel, it can cause significant problems with the skin in that area. However, if the injector is performing the procedure properly, this should occur very rarely. When doing this procedure, make sure to find an experienced physician who injects fillers on a regular basis. If done correctly, the results should be excellent.