[How the sun ages our skin. The dermis as the driving force].

Extrinsic factors (= environmentally induced skin aging) lead to both epidermal and dermal changes. Recent investigations have shown that the dermis plays the decisive role, at least for skin aging caused by ultraviolet (UV) radiation. Exposure to UV radiation results in an accumulation of damage to the mitochondrial DNA of dermal fibroblasts and thus an altered gene expression of the affected cells, which chronically drives both the dermal (e.g., wrinkle formation) and epidermal (atrophy, barrier dysfunction) aging process. This knowledge is currently being used to develop highly effective cosmetic strategies to reverse the skin aging process.