In the shadow of the wrinkle: theories.

As time passes, wrinkles typically appear. These skin depressions that become deeper and deeper draw more and more coarser lines on almost all the visible parts of aging individual's skin. They are indeed the most obvious and maybe disliked signs of skin aging, and thus, preventing and treating them are a major topic for dermo-cosmetic laboratories. However, the cause and occurrence mechanism of these simplistic looking lines are not yet fully understood. Wrinkling is thought to be a complex biophysical process resulting from repeated strains on a progressively, structurally and biochemistry altered aging skin with impaired mechanical properties. Focus is made on the specific histological features of the wrinkle compared to the surrounding aging skin. The numerous age-related changes in human skin that are supposed to be involved in wrinkling are briefly reviewed, and the current theories on wrinkle formation linked to these changes are also discussed.

In the shadow of the wrinkle: experimental models.

Research on aging has run for decades, and knowledge on the biologic process of skin chronological and photoaging is still increasing thanks to read across results generated between human, animal, and in vitro studies. However, wrinkles should not be considered to result only from the aging process. There are few reports on specific wrinkle histological features compared to the surrounding skin, and there is thus a need in really wrinkling skin animal and in vitro models. UV-irradiated Hr mouse is a good model because it develops wrinkles. Nevertheless, as mouse skin is somehow different from human skin, the innovative model of wrinkling human skin xenograft on SCID mice seems to be really promising. Concerning in vitro and ex vivo models, although there have been considerable advances in reconstructing realistic aged skins, there is still a lack of in vitro wrinkling skin model, and unfortunately, this gap will probably be difficult to fill.