Visualizing the molecular landscape of skin: applications and perspectives of mass spectrometry imaging.

Mass spectrometry imaging (MSI) has emerged as a powerful tool in dermatological research due to its high sensitivity, label-free detection, and ability to simultaneously analyze multiple molecular species. This review systematically summarizes recent advancements in the application of MSI for visualizing both endogenous metabolites/biomacromolecules and exogenous compounds in the skin. Firstly, the basics of MSI are introduced, including the different ionization sources and the general workflow of MSI experiments. Then, the applications of MSI in skin physiology and metabolism analysis and identification of molecular characteristics or potential biomarkers of skin pathological status are summarized. Furthermore, MSI is also widely used as a complementary method for skin penetration studies of topical pharmaceutical and cosmetic ingredients. Examples of MSI applications are presented to indicate the diverse fields MSI contributes to and emphasize the advantages of MSI compared to conventional techniques. Nevertheless, the limitations and challenges are also discussed. Overall, MSI is expected to further advance both dermatological research and clinical applications.