Skin loosens and sags with age mostly because the volume in the underlying structures — like tissue, fat, and bone — are lost. Collagen and elastin loss in the dermis due to ultraviolet light also contributes to aging. UV light decelerates production of new collagen and triggers enzymes that break down existing collagen.
Volume is the key factor that separates young faces and old faces, which is why a face lift procedure that is meant to tighten skin makes the skin look smoother — but not younger.
Research from the University of Rochester Medical Center suggests that major changes in the facial bone, especially the jaw bone, takes place when someone ages and influences the appearance. Aging is also affected by changes in brow and cheek bones. When the openings in the bones (formina), like those around the nose and eyes, widen as edges recede, the skin that is draped on them loses support and sags.
Another research reveals that there are nine fat compartments that are gradually lost with aging. The loss only speeds up when exposed to UV light. These compartments affect the support where the skin is draped. The compartments of the face are the nasolabial fat compartment, cheek fat compartments, forehead and temporal fat compartments, orbital fat compartments, and the jowl fat compartment.
These things drive the results of rejuvenation procedures. Volume has to be restored properly so that it allows the face to gain a working youthful look. Older faces have topographical irregularities due to bone and fat degradation, while younger faces have distinct smooth arcs. Having such, older faces reflect less light and produce more shadows, which is another aging factor.