[sharphall]

It's unlikely "natural" has anything to do with it. Compounds that occur naturally are often synthesized, but it's the same molecule as found in nature. (example: vanillin) There are some scent molecules that are totally new and not found in nature outside of our production, but "naturally occurring" is a broad category that can include all sort of things individuals are likely to be sensitive to even after removing all the "natural" chemicals that are actual poison.

[o11c]

Cyanide is probably a better example.

[IAmBroom]

Mmmm, almonds...