Collagen-containing fillers: alone and in combination.

Soft tissue fillers may be injected into facial skin to ameliorate the appearance of fine lines and wrinkles, to augment lips and hollow cheeks, and to correct other imperfections, ultimately producing a more youthful appearance. Animal- and human-derived collagen implants have been used successfully for soft tissue augmentation for several years. Bovine collagen fillers were the most popular injectable implants for nearly 2 decades in the United States. Although these are still used, human bioengineered collagen products and fillers that contain hyaluronic acid have become available and are now more commonly used than the bovine-derived products. This article discusses the rationale for using the various types of fillers in combination and describes techniques for combining these fillers.