Phagocytosing cells undergo a burst of oxygen consumption that is caused by an NADPH oxidase complex that assembles at the phagosomal membrane. Neutrophils and the other phagocytes create O2- (superoxide) by the one-electron reduction of oxygen at the expense of NADPH. A variety of soluble and particular stimuli induce extracellular superoxide production. Most of the oxygen consumed can be accounted for as hydrogen peroxide, which is formed from dismutation of superoxide radical. From these agents a large number of highly reactive microbicidal oxidants are formed, including HOCl (hypochlorous acid), which is produced by the myeloperoxidase-catalyzed oxidation of Cl- by H2O2; OH (hydroxyl radical), produced by the reduction of H2O2 by Fe2+ or Cu+; ONOO (peroxynitrite), formed by the reaction between O2- and NO, and many others [66]. Reactive oxygen species (ROS) comprises not only free radicals, such as superoxide radical, hydroperoxyl radical, hydroxyl radical, peroxyl radical etc., but also non-radicals, namely hydrogen peroxide, singlet oxygen, and hypochlorous acid. These reactive oxidants are manufactured not only as microbicidal agents, but they also impose cell damage.