Spectroscopic and Dynamic Studies of the Epidermal Chromophores trans-Urocanic Acid and Eumelanin

Photoaging and skin cancer can result from the exposure of skin to ultraviolet A (UV-A, 320-400 nm) radiation. The detailed chemical mechanisms by which these processes occur are not known, but they must begin with the absorption of a UV-A photon by one or more photoreceptor(s) within the skin. The situation is complicated by the lack of understanding of the photoreactions of many of the UV-A-absorbing molecules in skin. In this Account, we describe recent research efforts directed at elucidating the UV-A-induced photoreactivity of two light-absorbing epidermal photoreceptors: trans-urocanic acid and eumelanin.