The Delaney Amendment was the clause of United States food law that forbade the use in food of any additive shown to cause cancer in humans or animals. Added to the Federal Food, Drug, and Cosmetic Act in 1958, it set an absolute, zero-tolerance standard: if a food or colour additive was found carcinogenic at any dose, it could not be approved, regardless of how tiny the exposure. For decades it forced the banning of several colourings and sweeteners and shaped the politics of food safety on both sides of the Atlantic. The absolute rule eventually collided with improving science — detection methods could find vanishingly small risks — and in 1996 new pesticide legislation replaced the zero-tolerance approach with a “reasonable certainty of no harm” standard. The Amendment remains a landmark in the history of precautionary food regulation.