Sodium sulfite is a soluble sodium salt of sulfurous acid (sulfite). It is made industrially by reacting sulfur dioxide with a solution of sodium carbonate. In cosmetics and personal care products, sodium sulfite functions as an antioxidant preservative. It works by protecting the other ingredients in a formulation from oxidation, which is the loss of electrons. For example, when products are exposed to air, oxygen from the air is reduced, gaining electrons from ingredients such as fats and oils in the formulation. This is why sodium sulfite can be referred to as a reducing agent; it donates a hydrogen atom to the oxygen in order to protect the other ingredients. Oxidation results in rancidity, color changes, viscosity changes and deterioration of active ingredients in finished products. By adding an antioxidant preservative like sodium sulfite the product will be less susceptible to degradation when exposed to environmental elements.