Studies of nitrosamines indicate that they are carcinogenic.  It has been suggested that nitrites added to bacon, hot dogs, and sandwich meats to retard spoilage may cause stomach cancer.  In the stomach, the gastric acid (HCl) can react with nitrite ions to form nitrous acid.  The nitrous acid reacts with the amines present in foods to produce nitrosamines.

There is considerable controversy about the use of nitrites and their possible effect on the human body.  On the one hand, it is clear that processed meats must have preservatives to have a reasonable shelflife.  However, how much can we tolerate?  The amount of nitrites used in laboratory tests with rats in many factors of ten higher than that used in commercial food products.  Thus, the amount of nitrite ingested by most individuals is comparatively small, and we are exposed to may other possible cancer producing chemicals of more serious and proven concern, such as cigarette smoke.  Like may features of life, there are trade-offs that we have to make.  At this point, the carcinogenic potential of nitrites at the levels currently used in meats is not clear.