Introduction (max 125 words): Our skin is constantly exposed to solar radiation, high oxygen levels, and environmental pollutants. These are accelerant stress factors for premature skin aging, tissue inflammation, and photocarcinogenesis. Such oxidative stress activates cutaneous lipoxygenases and nonenzymatic lipid peroxidation. Oxidized lipids can act as danger-associated molecular patterns (DAMPs) and as members of the senescence-associated secretory phenotype (SASP), the signaling cocktail of senescent cells. Our study aims to target bioactive oxidized phospholipids of the SASP and expand the list of possible candidates. We present a systematic investigation of lipids and their chemically-driven oxidation products (oxLipS) generated in a controlled environment by reactive oxygen species (ROS) after UV exposure. OxLipS are analyzed by ESI and MALDI FTICR MS. Results are correlated to results from skin-equivalents investigated by MALDI imaging. Methods (max 100 words): Lipid standard solution (LipS) is comprised of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC) and the internal, not UV affected reference 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dinonanoyl-sn-glycero-3-phosphocholine (DNPC). Solar-like conditions were simulated by exposure to 0/80 J/cm2 of UVA radiation. Skin equivalents (3D cell cultures) were doped with a) LipS; b) LipS pre-exposed to UV (oxLipS); c) LipS and then exposed to UV; d) LipS and Fibroblasts again followed by UV exposure. A 7T scimaX FTICR MRMS (Bruker) equipped with a dual ESI/MALDI source was used for analyses. Direct infusion for ESI and skin equivalent sections mounted on ITO slides for MALDI Imaging using 1,5-Diaminonaphthalene as matrix.   Preliminary data (Results) (Max 250 words): We aim to investigate and characterize oxLipS generated via chemical pathways to deepen the knowledge for dermal tissue investigations. Oxidized products of PAPC (oxPAPC) result from reactions with peroxides, from hydroxylation, consecutive fatty acid chain cleavage or loss of arachidonic moiety, to name a few. DNPC and DPPC instead, cannot generate oxLipS, thus serving as internal standard for semi-quantitative information. ESI FTICR MS analysis provided crucial information on oxLipS generated by ROS formed in solution after UV irradiation. Accurate, high-resolution MS data allowed identification of newly formed species through database search and tentative structural assignment for m/z values not found in the database. LipS and oxLipS were investigated by MALDI FTICR MS to identify ionization effects. m/z values were compared between ESI and MALDI, and dilution series allowed for LoDs determination. These findings were translated to skin-equivalent samples by doping 3D cell cultures with LipS and oxLipS of known concentration and composition to study the effect of collagen on LoDs. This also mimics, to some extent, real-life conditions. Qualitative, semi-quantitative, and spatial information about oxLipS in tissue was generated by MALDI FTICR MS imaging. Finally, fibroblasts embedded in the collagen matrix together with LipS were also exposed to UV light to assess the additional effect of cells on lipid oxidation. Chemistry-driven PAPC oxidation will be superimposed by UV-induced biological effects and results were carefully considered for future research on human skin samples. The authors thank the Federal Ministry of the Republic of Austria and CHANEL Parfums et Beauté financial support.