Reduction potential (also known as redox potential, oxidation / reduction potential, ORP or E_{h}) is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts (V), or millivolts (mV). Each species has its own intrinsic reduction potential; the more positive the potential, the greater the species' affinity for electrons and tendency to be reduced.
Oxidation is not always understood, with many people thinking that oxidation is the process of adding oxygen to other substances. That is not the case. Oxidation is the process by which substances are destroyed. The electrons that hold a substance together are pulled off by the oxidizing chemical and thus the substance then comes apart, which of course, destroys it.
Reactive oxygen species (ROS) are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons. ROS form as a natural byproduct of the normal metabolism of oxygen and have important roles in cell signaling and homeostasis.[1] However, during times of environmental stress (e.g., UV or heat exposure), ROS levels can increase dramatically.[1] This may result in significant damage to cell structures. Cumulatively, this is known as oxidative stress. ROS are also generated by exogenous sources such as ionizing radiation.