Thiosulfuric acid is a chemical compound with the formula H2S2O3. It is a weak acid that contains sulfur and oxygen, and it is often encountered in its salt forms, known as thiosulfates. Thiosulfuric acid is typically produced through the reaction of sulfur dioxide with sodium sulfite or sodium thiosulfate. This acid is primarily used in various industrial applications, including photography and water treatment. It plays a role in the sulfur cycle and can act as a reducing agent in chemical reactions. Due to its instability, thiosulfuric acid is not commonly isolated in pure form.