Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula Na2S2O3·(H2O)x. Typically it is available as the white or colorless pentahydrate (x = 5), which is a white solid that dissolves well in water. The compound is a reducing agent and a ligand, and these properties underpin its applications.[2] Uses Sodium thiosulfate is used predominantly in dyeing. It converts some dyes to their soluble colorless "leuco" forms. It is also used to bleach "wool, cotton, silk, ...soaps, glues, clay, sand, bauxite, and... edible oils, edible fats, and gelatin."[2] Medical uses Main article: Sodium thiosulfate (medical use) Sodium thiosulfate is used in the treatment of cyanide poisoning.[3] It is on the World Health Organization's List of Essential Medicines.[4][5] Other uses include topical treatment of ringworm and tinea versicolor, [3][6] and treating some side effects of hemodialysis[7] and chemotherapy.[8][9] In September 2022, the U.S. Food and Drug Administration (FDA) approved sodium thiosulfate under the trade name Pedmark to lessen the risk of ototoxicity and hearing loss in infant, child, and adolescent cancer patients receiving the chemotherapy medication cisplatin.[10][11] Photographic processing See also: Collodion § Wet-plate collodion photography In photography, sodium thiosulfate is used in both film and photographic paper processing as a fixer, sometimes still called 'hypo' from the original chemical name, hyposulphite of soda.[12] It functions to dissolve silver halides, e.g., AgBr, components of photographic emulsions. Ammonium thiosulfate is typically preferred to sodium thiosulfate for this application.[2] The ability of thiosulfate to dissolve silver ions is related to its ability to dissolve gold ions.