Chemical burns can be caused by over 25,000 substances,[2] most of which are either a strong base (55%) or a strong acid (26%).[36] Most chemical burn deaths are secondary to ingestion.[2] Common agents include: sulfuric acid as found in toilet cleaners, sodium hypochlorite as found in bleach, and halogenated hydrocarbons as found in paint remover, among others.[2] Hydrofluoric acid can cause particularly deep burns that may not become symptomatic until some time after exposure.[37] Formic acid may cause the breakdown of significant numbers of red blood cells.[22]