An endogenous tryptophan photo-product, FICZ, is potentially involved in photo-aging by reducing TGF-β-regulated collagen homeostasis

Ultraviolet (UV) radiation has major adverse effects on the outermost layer of the body, namely, the skin. The mechanisms by which UV causes photocarcinogenesis and photo-aging are well established. UV-mediated responses directly induce deleterious cell damage by generating DNA photo-products in the nucleus, namely, reactive oxygen species (ROS) and organic free radicals [1–4]. A variety of chromophores and photosensitizers have been reported to be produced in the skin in response to UV exposure [5,6].