Facial aging is a complicated process in which both intrinsic and extrinsic factors lead to changes in physiologic function and loss of structural integrity. Decreased dermal thickness is the hallmark of extrinsic aging, with accompanying skin laxity and changes in both pigmentation and texture.4
Chronic ultraviolet exposure and resultant solar elastosis is responsible for 80% of skin aging.5
The effects of sun exposure are many, including a dramatic decrease in collagen and an alteration of the extracellular matrix (ECM). The ECM is made up of collagen, elastin, and hyaluronic acid (HA); proteoglycans, and glycosaminoglycans.6
Support of the ECM is lost with the formation of a disorganized elastic tissue network, and there is a reduction in the production of all components of the ECM.7
Matrix metalloproteinases are responsible for the continual breakdown of collagen but can be downregulated via a stretch receptor in the collagen-forming fibroblasts.4
All of these ultrastructural changes lead to physiological changes that result in the appearance of coarse rhytids especially in areas overlying the mimetic musculature. Repetitive facial movements, especially in areas of sun exposure, give rise to the hallmark deep aging lines in the glabella, forehead, and lateral canthal areas.