Lipids are essential molecules for cellular signaling, metabolism, and key components of our cells. At the skin level, exposure to solar radiation, high oxygen levels, and environmental pollutants leads to premature skin aging, tissue inflammation, and photocarcinogenesis. This oxidative stress activates cutaneous lipoxygenases or causes nonenzymatic lipid peroxidation, thus forming oxidized lipids (oxLipS). We present a systematic investigation of lipids and their non-enzymtic oxidation products generated in a controlled environment after UV exposure. Untargeted OxLipS analysis was performed on a dual-source ESI/MALDI 7T scimaX FTICR MRMS (Bruker). ESI was used for species identification, while the MALDI Imaging platform (MSI) complemented the analysis with spatial localization in tissue. A lipid standard solution (LipS), PAPC and not UV affected references DPPC and DNPC in chloroform were exposed to solar-like conditions (UVA radiation). Direct infusion ESI experiments of the LipS generated crucial information on oxLipS species produced by ROS formed in solution. Accurate, high-resolution MS data allowed identification of known and newly formed species via database search (LipidMAPS). Skin biopsies were mounted on ITO slides for MALDI MSI. Different sample preparation methods after tissue washing have been investigated, and instrument parameters adapted for optimized FT ICR imaging [1,2]. Selected m/z values were compared between ESI and MALDI, thus aiding the translation of ex vivo experiments to in vivo MALDI MSI results. Several oxLipS were localized, visualized, and identified in skin section samples. REFERENCES [1] Narzt MS et al. (2021) J Invest Dermatol. 141(4S):993-1006.e15. doi: 10.1016/j.jid.2020.11.020 [2] Tiquet et al. (2022) Anal. Chem. , doi.org/10.1021/acs.analchem.2c00754