Sources of information. The World Health Organisation publishes papers on the maximum levels recommended in foodstuffs. Their deliberations are ongoing and from time to time new reports are issued. The Council of Europe publishes similar guidelines. The FDA in the United States has lists of GRAS status ingredients for foods which include some essential oils.
Medicines act does that.
Well they have many sources of information to draw on, or if they are uncertain, they will commission independent studies. Many essential oils were listed in several National pharmacopoeias around the turn of the Century because they were commonly used in medicinal preparations. However, subsequently a significant amount of scientific investigations have been undertaken, particularly in many universities around the world. Some of this work has been co-ordinated for regulatory authorities, and some experiments simply for independent academic studies. Finally, they have commissioned significant research evaluations of fragrance materials.