Reactive oxygen species (ROS) such as superoxide and hydrogen peroxide are continually produced during metabolic processes. ROS generation is normally counterbalanced by the action of antioxidant enzymes and other redox molecules. However, excess ROS can lead to cellular injury in the form of damaged DNA, lipids and proteins.

Excess ROS must be promptly eliminated from the cell by a variety of antioxidant defense mechanisms. Cellular antioxidant enzymes and other redox molecules serve to counterbalance ROS generated in the cell.