ABSTRACT
The skin forms the outermost layer of the body, and changes in its properties with aging are directly linked to changes of appearance, such as wrinkling and sagging. Natural or intrinsic skin aging can be worsened by the accumulation of damage due to exposure to the ultraviolet component of sunlight (photoaging). Aging-related changes of skin elasticity are due to the deterioration of the extracellular matrix in the dermal layer, including alterations in elastic fibers (solar elastosis and glycation), and in the balance of synthesis/degradation of collagen and glycoproteins such as versican, decorin, biglycan, glycosaminoglycans (GAGs) and hyaluronic acid (HA). Matrix metalloproteinases (MMPs) and their inhibitors are key players. Fibroblasts regulate these processes, so changes of fibroblasts with aging are critical and may lead to a negative spiral of dermal aging (senescence-associated secretory phenotype; SASP). Furthermore, the subcutaneous adipose layer controls the condition of the dermal layer by secreting multiple factors. Skin also contains many appendages, such as sweat glands and sebaceous glands, which contribute to skin surface homeostasis by secreting sweat and sebum, respectively. Here, we summarize the physical and physiological changes of skin with aging, ranging from basic concepts to the latest knowledge relevant to cutting-edge skincare research.
