Believe it or not, it is not known how many basic classes of odors people can sense. Well, it may be ten! This comes from a mathematical analysis of odor profiles without regard to molecular physiology. If this were reflected in the biology of odor detection, the multiplicity of specific perceived odors would arise from differential and "combinatorial" activation of sets of distinct olfactory receptors. However, even the basic set of general categories could be broader, as the authors of the original article state:
"Our study has some limitations that should be noted. Chief among these is the small size of the odor profiling data set used relative to the much larger set of possible odors, which may limit the generality of our findings. In future studies, it will be necessary to extend the NMF framework to larger sets of odors than the 144 investigated presently, such that a more complete and representative sample from odor space is obtained."
So who knows? We return to: believe it or not, it is not known how many basic classes of odors people can sense.
What's That Smell? Ten Basic Odor Categories Sniffed out With Math
Sep. 18, 2013 — Taste can be classified into five flavors that we sense, but how many odors can we smell? There are likely about 10 basic categories of odor, according to research published September 18th in the open access journal PLOS ONE by Jason Castro from Bates College, Chakra Chennubhotla from the University of Pittsburgh, and Arvind Ramanathan from Oak Ridge National Laboratory. The researchers used advanced statistical techniques to develop an approach for systematically describing smells.
The team identified 10 basic odor qualities: fragrant, woody/resinous, fruity (non-citrus), chemical, minty/peppermint, sweet, popcorn, lemon and two kinds of sickening odors: pungent and decayed.