The most common fillers, such as the JUVÉDERM and Restylane product lines, use the same active ingredient—hyaluronic acid (HA). Hyaluronic acid is a sugar that’s naturally found in the skin. It absorbs water, so when injected, it acts like a sponge and expands to fill wrinkles and folds. Hyaluronic acid-based fillers are volumizers. Other fillers such as Sculptra and RADIESSE are called biostimulators because they stimulate the production of new collagen.