Fillers are substances that are injected into the skin to add volume and fill in wrinkles, folds, and other depressions. The most common fillers are made from hyaluronic acid, a natural substance that is found in the skin. Hyaluronic acid fillers are FDA-approved and are considered safe and effective for most people. The results of fillers typically last for several months to a year, depending on the type of filler used and the area of the face that is treated. Some common areas for filler injections include the cheeks, lips, and under-eye area.