 Oxygen can be transformed into reactive oxygen species, ROS, upon reaction with electrons, which have both beneficial and harmful effects on cells. While high concentrations of ROS can cause nonspecific damage to proteins, lipids, and nucleic acids, low-to-intermediate concentrations exert their effects through regulation of cell signaling cascades. ROS play crucial roles in normal physiological processes such as redox of protein phosphorylation, ion channels, and transcription factors, as well as biosynthetic processes like thyroid hormone production and extracellular matrix crosslinking. There are multiple sources and degrading systems for ROS, and diseases caused by a surplus or lack of ROS can have varying clinical outcomes. Antioxidant supplementation has been largely ineffective in clinical studies, while specific inhibition of ROS-producing enzymes shows more promising clinical efficacy. This article was authored by Katharine Brieger, Stefania Shivoni, Francis J. Miller Jr., and others. We are article.tv, links in the description below.