Endogenous Photosensitizers in Human Skin

Endogenousphotosensitizers play a critical role in both beneficialand harmful light-induced transformations in biological systems. Understandingtheir mode of action is essential for advancing fields such as photomedicine,photoredox catalysis, environmental science, and the development ofsun care products. This review offers a comprehensive analysis ofendogenous photosensitizers in human skin, investigating the connectionsbetween their electronic excitation and the subsequent activationor damage of organic biomolecules. We gather the physicochemical andphotochemical properties of key endogenous photosensitizers and examinethe relationships between their chemical reactivity, location withinthe skin, and the primary biochemical events following solar radiationexposure, along with their influence on skin physiology and pathology.An important take-home message of this review is that photosensitizationallows visible light and UV-A radiation to have large effects on skin.The analysis presented here unveils potential causes for the continuousincrease in global skin cancer cases and emphasizes the limitationsof current sun protection approaches.