Figure 5.

Skin aging. Over time, aging skin undergoes a number of alterations that contribute to dysfunction. In addition to chronological aging, certain external stimuli can accelerate aging; these include ultraviolet (UV) and γ-irradiation and exposure to pollution and other environmental insults, such as cigarette smoke [11,50]. Skin function declines with age. Reduced extracellular matrix proteins in the dermis result in wrinkling, elastosis and thinner skin (since the dermis represents 90% of the skin thickness [52]), and abnormalities in pigmentation lead to lentigines (liver spots) and ephelides (freckles) [10]. Epidermal dysfunction results in a thinner epidermis (due to decreased proliferation of aged epidermal keratinocytes) and xerosis (from reduced production of proteins involved in skin hydration and deficiencies in the epidermal permeability barrier) [53]. Telangectasias and thinning of the subcutaneous fat (in some but not all regions of the body) [11,54] also characterize aged skin. Created with Biorender.com.