One more caveat, only plants which cause problems are listed. Lots of plants aren t listed at all. I say this because it is easy to conclude that everything is an allergen from what one reads here. MedLine and other web sites and also indices to medical or cosmetic industry journals are good sources for newer information. Negative reactions to essential oils are dose dependent.
Larger doses create larger problems.
Successive doses create sensitization. Of course, some oils cause more problems than others. First, we need to understand the nature of the problems, and the limits of this article. Some of what I say is also relevant to internal situations. Please remember that inhalation is an internal use of essential oils.