sulfurous acid (H2SO3) /sul″fərəs/ , a weak inorganic acid formed by dissolving sulfur dioxide in water, used as a chemical-reducing and bleaching agent. It has been used in medicine in skin lotions and nasal and throat sprays. Sulfites formed by the acid may be included in antiseptics, antifermentatives, and antizymotics. Sulfurous acid is stable only in aqueous solutions; it decomposes into sulfur dioxide and water on standing. It is a major component of acid rain.
