Play media Redox (reduction–oxidation, pronunciation: /ˈrɛdɒks/ redoks or /ˈriːdɒks/ reedoks) is a type of chemical reaction in which the oxidation states of atoms are changed. Redox reactions are characterized by the transfer of electrons between chemical species, most often with one species (the reducing agent) undergoing oxidation (losing electrons) while another species (the oxidizing agent) undergoes reduction (gains electrons). The chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. In other words: Oxidation is the loss of electrons or an increase in the oxidation state of an atom by another atom, an ion, or a molecule. Reduction is the gain of electrons or a decrease in the oxidation state of an atom by another atom, an ion, or a molecule. For example, during the combustion of wood, electrons are transferred from carbon atoms in the wood to oxygen atoms in the air. The oxygen atoms undergo reduction, gaining electrons, while the carbon atoms undergo oxidation, losing electrons. Thus oxygen is the oxidizing agent and carbon is the reducing agent in this reaction. Although oxidation reactions are commonly associated with the formation of oxides from oxygen molecules, oxygen is not necessarily included in such reactions, as other chemical species can serve the same function. Redox reactions can occur relatively slowly, as in the formation of rust, or much more rapidly, as in the case of burning fuel. There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), and more complex processes such as the oxidation of glucose (C6H12O6) in the human body.