Chemiexcitation in Ex Vivo Porcine Skin Model

Chemiexcitation, the formation of electronically excited states via oxidative chemical reactions, has emerged as a potentially important contributor to skin photobiology beyond direct damage caused by ultraviolet (UV) radiation. This study investigates the hypothesis that UV radiation induces chemiexcitation in skin through the formation of triplet excited carbonyls, which may transfer energy to melanin and contribute to oxidative stress even after the termination of UV exposure. Using porcine skin as a model, we demonstrate that UV exposure leads to lipid peroxidation and the subsequent formation of organic radicals, including carbon-centered (alkyl) and oxygen-centered (peroxyl and alkoxyl) species, as detected by EPR spin-trapping spectroscopy. HPLC-MS analysis revealed that short-chain carbonyl compounds, such as formaldehyde and acetaldehyde, are the predominant electronically excited species in direct chemiexcitation. These triplet carbonyls can transfer their excitation energy to melanin through photon emission (radiative transfer) or direct electron exchange (non-radiative transfer), forming melanin-based secondary excited states via indirect chemiexcitation. These findings highlight a novel, light-independent mechanism of post-UV exposure oxidative damage in the skin and suggest a possible role for chemiexcitation in processes such as photoaging and photocarcinogenesis.