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INTRODUCTION

Aging in the face is a multifactorial process involving one’s genetic make-up as well as exogenous factors, and leads to various changes in the skin including vascular and pigmentary alterations, rhytide formation, volume loss, and bony structural changes of the face. To better understand how to globally rejuvenate the skin, it is helpful to understand the various changes in the skin that contribute to the appearance of aging. With the advancement in aesthetic therapeutics available to physicians, these changes can be targeted with various procedures including the use of botulinum toxin, injectable fillers, and light and laser therapies.

SKIN AND AGING

Intrinsic and Extrinsic Aging

With aging, skin undergoes physiologic and morphologic changes that can be categorized as intrinsic aging due to endogenous factors and extrinsic aging due to exogenous factors. Intrinsic aging is influenced mainly by genetics, cellular metabolism, and hormone environment. Histopathologically, intrinsic aging exhibits decreased amounts of normal collagen and elastic fibers, atrophy of the extracellular matrix, diminution of the dermal thickness with decreased number of fibroblasts, thinning of the subcutaneous fat, slow replacement of lipids, reduced function of skin appendages (e.g., sebaceous glands, sweat glands, apocrine glands), and epidermal atrophy.1–4 Extrinsic aging mostly involves sun-exposed skin and is primarily caused by ultraviolet radiation, ionizing radiation, toxins, chemicals, and pollutants. Among these, cumulative ultraviolet light exposure and tobacco use appear to be more influential in aging skin.5,6 The morphologic changes demonstrated in extrinsic aging include impaired proliferation and differentiation of keratinocytes, increased levels of dysfunctional glycosaminoglycans and proteoglycans, increased collagen degradation with sparse distribution of collagen fibers, accumulation of abnormal elastic tissue in the dermis, reduced number of anchoring fibrils, and thickening of the epidermis in the early stages.1–4 The thickened epidermis is thought to be due to a chronic wound-like state in which there is a continual attempt to repair the skin.3,4 These changes of both intrinsic and extrinsic aging ultimately lead to the decrease in skin elasticity, overall volume loss caused by both dermal and subcutaneous atrophy, and fine wrinkle formation seen with aging in the skin.

Rhytides

The presence of rhytides, whether dynamic or static, contributes to the appearance of aging in facial skin. Rhytides are formed as a result of both cumulative ultraviolet light exposure and repetitive muscle contractions. With exposure to ultraviolet light over time, there is an accumulation of abnormal elastic tissue in the dermis,1,3 which leads to reduced elasticity and subsequent impaired retightening of the skin—seen clinically as rhytides. In early photoaging, these rhytides are apparent only with dynamic movement of the face, often on the forehead, the lateral canthi (crow’s feet), near the oral commissures, and over the zygomatic arch and malar eminences. In more advanced photoaging, with the added influence of repetitive muscle contractions, these rhytides are visible when the face is at rest and are known ...

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