Human Skin Aging: Physiology and Pathophysiology.

Skin is the outermost layer which covers all organs of the body. Skin can be divided into three layers, including epidermis, dermis and hypodermis. Similarly to many organs of the body, skin also experiences biological process that could not resist aging. There are the following two types of human skin aging: endogenous and exogenous. Endogenous aging involves a series of physiological changes that gradually occur over time and are influenced by genes and hormones. In contrast, extrinsic aging (or exogenous aging), also known as photoaging, involves significant structural and functional changes due to external factors, mainly due to lack of sun protection, smoking, air pollution, lifestyle, etc. Skin aging not only affects the appearance but also makes the skin more sensitive to geriatric skin diseases. In order to treat geriatric skin disease effectively and appropriately, it is crucial to study skin aging from a clinical and histological perspective.