Not all the worlds 250,000 flowering species are safe to use in aromatherapy. In fact the number which can be used without mishap while following sensible guidelines is less than 150. The most poisenous flowering plant in the world is the Himalayan monkshood (Aconitum ferox). This plant is so poisenous it can kill just by being in close enough proximity to be smelt. On contact the poisen enters the skin. There is no antidote.
Essential oils were subject to rigourous examination as part of a series of over 1000 monographs published by the Research Institute of Fragrance materials in the Food and Cosmetic Toxicology journal some 40 years ago. this research established clear guidelines for their use. Test results were organised by 5 categories of hazards: Oral toxicity, Dermal toxicity, Primary irritation, Contact sensitisation and phototoxicity.
When properly used essential oils have been found to be beneficial in helping with various health problems. However like all biologically active substances they are not risk free and misuse may cause severe adverse reactions. They occur in plants in concentrations as low as 0.01% but are sold in 100% pure form so must be diluted before use.
A generally safe concentration is 2% diluted in unrefined fixed oils (such as grapeseed, sunflower, olive or almond oil). Certain oils can be used undiluted for example on a spot or wart.
It is not recommended to eat the oils because of the potential complications involved in doing so by the inexperienced. Individual reaction to the oils can vary widely. All essential oils are irritants to the mucous membranes and practically insoluable in water. Honey is also useless. If using essential oils it is always prudent to consult professionals trained in their use. This applies also to the fixed oils some of which should not be eaten.