Aging of organs starts from the time of birth and continues throughout life. Aging of skin can be divided into two distinct types—intrinsic aging and extrinsic, based on the fact that the skin is the outermost organ exposed to the external environment. However, despite their different histological features and triggers, intrinsic and extrinsic aging share common biochemical mechanisms. β-galactosidase, p16^INK4a, and senescence-associated secretory phenotype (SASP) factors are detected in skin cells as biomarkers of senescence. In particular, inflammatory cytokines, the constituents of SASP, play pivotal roles in “inflammaging” which is a concept involving the relationship between aging and low-grade inflammation. In this review, the features of skin aging and its underlying mechanism of skin aging are summarized.

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