The author examines the construction of the first tools for regulating food additives and contaminants, an industry which - second only to the nuclear industry and along with occupational health - was one of the main loci for reflection on and development of tools for regulating toxicants in the latter half of the twentieth century. This construction took place within international scientific committees, notably those created by UN organizations such as the FAO and the WHO. In this paper she highlights the importance of looking at how some of the foundations of international systems for regulating toxicants, which developed significantly in the second half of the 1970s, were laid during the preceding two decades. She also highlights how certain young scientists from Western Europe tried to take advantage of the construction of these international organizations to build spaces of legitimacy for their disciplines, especially toxicology, while developing their own careers. Finally, the approach via the construction of regulatory tools shows the contradictory logics underpinning the early development of the international expertise. Within a few years, from the late 1950s to the early 1960s, the concern of these 'international experts' to guarantee a high level of protection for public health had to make way for economic priorities. The experts were convinced that it was impossible to set a threshold for carcinogens beneath which no effect could be found, and that it was therefore essential to ban these substances in food in order to guarantee the protection of public health. Nevertheless they eventually produced limit values for carcinogenic substances. They therefore contributed to the creation of a dynamic in which it was constantly necessary to find the means to justify the contradiction between the claim of protecting public health, and approval of the use of a multitude of dangerous substances. The risk technology that was gradually deployed throughout the 1980s was developed precisely to try to resolve that contradiction.