Skin aging is the result of two main biological processes:
the normal passage of time, chronoaging, and aging due to environmental stress factors, in particular UV radiation and free radicals, called photoaging. These processes cause visible alterations to skin, such as loss of firmness and elasticity, the appearance of lines and wrinkles, and uneven pigmentation
Skin firmness and elasticity is determined mainly by the dermis, where support structures such as collagen and elastin can be found, as well as other components such as hyaluronic acid which provide volume and compactness. As skin ages, or is damaged by UV radiation, its ability to renew itself decreases.
Stem cells, which are responsible for producing new skin cells, decrease and their activity slows, as does that of fibroblasts, which synthesize the main components of the dermis. Fewer dermal support structures are thus available to maintain skin firmness and elasticity, and skin progressively loses tone.
As the thickness and resilience of the dermis decreases, lines and wrinkles begin to appear on the surface of the skin. Lines and wrinkles are also caused by alterations to the epidermis where the renewal of keratinocytes slows and the skin barrier function is diminished, leading to surface roughness, dryness and increased sensitivity.
Here again stem cells play an important role in determining the production of young, healthy cells, and delicate exfoliation can promote cell turnover and restoration of natural physiological conditions.