Since NADPH oxidase (NOX) 4, one of the important pulmonary ROS sources that is upregulated in IPF and promotes alveolar epithelial cell death [69] and fibroblast activation [70, 71], mainly produces H2O2 it can be suggested that quercetin cannot counteract NOX4-induced fibrotic outcomes. This evidence concerns the gene FMO5 and idiopathic pulmonary fibrosis.