MMP9 and skin cancer: Interacts with stratum corneum lipids, proteins, and DNAIncreases ROS HO−, O2−, and H2O2 [40,50,51,52]4-HNE adducts form and induce further lipid peroxidationActivation of NF-кβ aryl hydrocarbon receptor Ahr and HSPs enhance release of IL-8, COX2 (ozone-induced inflammation) [40,48,53,54,55,56,57]Increases in MMP-2 and MMP-9 (ozone-induced aging) and skin cancer progression, respectively [58]