If you have heard anything at all about smell training, you have probably heard about the four essential oils recommended: lemon, rose, clove and eucalyptus. I’d like to write a bit here about how they were originally chosen, and how they have become the four oils of choice for smell training.
A book was written in 1915 by a German psychologist called simply “Der Geruch” (Smell). This is a lengthy discourse written in an attempt to understand smells and pin them down. The author tried to classify smells, and see where the main groupings intersected, and also which smells overpower other smells (onion and camphor for instance. Hardly a fair fight). Would comparing and contrasting smells could lead to anything meaningful? It all seems a bit out of date now—you can download a pdf copy through Google books—but you can see that there was a genuine attempt to understand not so much the “sense of smell” as smells in general.
The comment that I thought was most memorable comes in the foreword: “the composition of a perfume cannot depend upon objective chemical characteristics, but must take into account subjective, emotional effects”. This comment interests me because as a largely recovered post-viral anosmic, the thing that shines through loud and clear when I smell perfume is an unemotional understanding of individual constituents, but the poetry and emotional impact of the combination is largely lost on me.
So how did this book lead us forward into the 21st century to smell training with lemon, rose, clove, and eucalyptus? Henning theorises about a prism of smells, defining six groupings: floral, putrid, fruity, burned, spicy and resinous. If you imagine a column with three sides, and one of these smell designations at each corner, you will have a picture in your mind of the author’s smell prism.
Fast forward to the dawn of smell training as a therapy for people with smell loss. Given that smell training with something putrid and something burned would be inconvenient and probably unpleasant, the four remaining smell groups were left: floral (rose), fruity (lemon), spicy (clove) and resinous (eucalyptus).
Because of the way scientific research works, these four essential oils were reused in many of the subsequent studies on smell training. Using the same oils kept a level playing field when considering how patients were responding. And so these four oils became the norm for smell training.
When I started smell training, I was unable to detect rose at all. Clove was so revolting to me that I had to really steel myself to do it. In time it became bearable and now is pleasant. Lemon was the first that felt real to me, it was the first where I felt I could say “this smells the way I expect it to smell, or sort of”. Eucalyptus always packed a big trigeminal punch for me. It’s that blast of Vicks you get when you try it, and it is important to say that the trigeminal response is not smell—this is another nerve at work inside your nose alerting you to a sensation rather than an odour.
When people ask me whether it is important to use these four oils or whether they should feel free to try others, I always say they should feel free to smell train freely with whatever they feel makes them happiest. The classic four, first described by Professor Hummel in 2009, are just the most frequently described in the literature. The golden rules are: Do it twice daily. Do it mindfully. And try not to shy away from smells that have become disgusting through parosmia. Boxing your way through the bad smells seems to be, from my own experience and that of others in this group, the best way to get around the misery of parosmia.