The face loses its volume as we age. In medical terms it’s called atrophy. The tissues are “shrinking” at all levels. Bone, cartilage, muscles, fat and skin are losing volume and this results in a hollow face, wrinkles and sagging skin. In order to correct that volume loss we must act on all levels. Unfortunately, the anatomy of the face is a complex topic. Deep structures, superficial structures, mobile zones and fixed zones are all part of the landscape of the facial structure. We even have zones where only the smoothing effect is desired, but not the volume correction. The degree of softness of the lost tissue is different on each location too. As we are using “HA fillers” as the primary material to correct a diversity of lost tissues such as bone, cartilage, fat, muscles and skin, we must adapt the viscoelastic (rheological) properties of the filler to the quality of the lost tissue.