In chemistry and biology, reactive oxygen species are highly reactive chemicals formed from diatomic oxygen, water, and hydrogen peroxide. Some prominent ROS are hydroperoxide, superoxide, hydroxyl radical, and singlet oxygen. ROS are pervasive because they are readily produced from O₂, which is abundant. ROS are important in many ways, both beneficial and otherwise. ROS function as signals, that turn on and off biological functions. They are intermediates in the redox behavior of O₂, which is central to fuel cells. ROS are central to the photodegradation of organic pollutants in the atmosphere. From Wikipedia
