Histotoxic hypoxia (also called histoxic hypoxia) is the inability of cells to take up or use oxygen from the bloodstream, despite physiologically normal delivery of oxygen to such cells and tissues.[1] Histotoxic hypoxia results from tissue poisoning, such as that caused by cyanide (which acts by inhibiting cytochrome oxidase) and certain other poisons like hydrogen sulfide (byproduct of sewage and used in leather tanning).