The chemical reaction between a substance and oxygen is a type of oxidation reaction; oxygen can react chemically with many substances. The effect of gaining electrons is called reduction. Oxidation in a narrow sense refers to the combination of substances with oxygen; reduction refers to the effect of substances losing oxygen. The oxidation value increases during oxidation; the oxidation value decreases during reduction. Both oxidation and reduction refer to reactants (molecules, ions or atoms). Oxidation is also called oxidation or oxidation reaction. When organic matter reacts, the action of introducing oxygen or dehydrogenation of organic matter is called oxidation; the action of introducing hydrogen or losing oxygen is called reduction. Oxidation in which substances react slowly with oxygen and emit heat without emitting light is called slow oxidation, such as metal rust, biological respiration, etc.