Injectable dermal fillers are approved treatments that physically fill lines, wrinkles, and hollow areas by adding volume to certain areas of the face, including the cheeks, lips, or nasolabial folds, to enhance facial contours and restore a youthful appearance. Hyaluronic acid (HA) is the most common type of filler. HA is a substance naturally found in your skin that attracts water, giving skin a plump and hydrated look.