A reducing agent is a substance that loses electrons in an oxidation-reduction reaction. Generally speaking, the reactant with higher valence of a substance is a reducing agent. Reducing agent itself is reductive and oxidized, and its product is called oxidation product. Reduction and oxidation reactions are carried out at the same time, that is to say, the reducing agent is oxidized and becomes the oxidation product at the same time of redox reaction with the reduced substance.