Odor perception is a complex and highly subjective process, influenced by physiological, genetic, psychological, and cultural factors.
An emblematic example of this variability is the 2-nonenal molecule, an aldehyde found in many beverages and foods. When different people are asked to describe the smell of this molecule, responses can vary widely: some associate it with a cucumber or vegetable aroma, others may perceive notes of melon, spice, mold, or bug, while still others may not recognize it at all. This diversity in descriptions raises an interesting question: why does the same olfactory molecule elicit such different semantic descriptors? The reasons are varied: as the intensity of the molecule changes, the olfactory perception changes; there are individual differences in the olfactory threshold; emotions and experiences of each of us affect perception.
Unlike vision, where a color remains constant regardless of its intensity (it depends on the length of the reflected light wave), olfactory perception can change qualitatively as the concentration of the odor molecule changes. An example of this is furaneol, a molecule that at low concentrations can be perceived with a strawberry aroma, while at higher concentrations it can take on notes of caramel, that is, it veers into a completely different smell. This phenomenon indicates that the intensity of the odor not only affects its strength but can completely alter its perceived quality.
Each individual, then, has a unique olfactory sensitivity, determined by genetic and environmental factors. This variability means that the minimum concentration of a molecule is required to be perceived as the olfactory threshold-varies from person to person. As a result, while one person may detect the aroma of strawberry at a certain concentration, another may not perceive it at all or identify it as a different smell. This difference in olfactory threshold contributes to the diversity of descriptions for the same odor molecule or non-perception of it. It is also known that the olfactory threshold varies over time in each person: therefore, a person who would smell and describe 2-nonenal as cucumber today might smell it as grass tomorrow depending on psychophysical conditions. But it doesn't end there: our sensitivity to odors can change over time due to factors such as olfactory adaptation, where prolonged exposure to a specific odor reduces our ability to perceive it. For example, a person who works daily in a bakery might become less sensitive to the aroma of vanillin than someone who rarely encounters it. In addition, physiological conditions such as hormonal changes, age, or health status can affect olfactory perception, leading to different descriptions of the same smell at different times in one's life.
Another reason for the diversity of olfactory descriptions lies in the fact that personal experiences and emotional associations play a crucial role in odor perception. The sense of smell is closely linked to the limbic system, the part of the brain responsible for emotions and memory. It is interesting to bring to light the example of the eugenol molecule. This molecule is found both in some medicines, for example for dental care, and in some clove dishes. That is why it is easily recognized even blindly by many people, but it can recall very different emotions: some may associate its aroma with the dentist, and others with good food. Both of these descriptions are valid. Therefore, an individual who has pleasant memories related to the aroma of cloves might describe this smell as comforting and stimulating. Conversely, a person who had negative experiences associated with this aroma might perceive it as less pleasant. These personal mnemonic associations of a molecule to a semantic label depend on the experience we had when we perceived it and particularly on the quality and intensity of the emotion we felt at the time. Depending on what stuck most in our emotional memory, we will describe the smell as “hospital/dentist” or as “clove/spice.”
We must then consider that the sense of smell is very powerful, but it is not possible to identify a smell unless we have smelled it before and named it, just as it would be impossible to name a song that we had never heard before. Therefore, our brain will match a new smell with the memory that comes closest to it. For this reason, to expand our “library of smells,” it is useful to train our olfactory memory, just as from an early age we have trained ourselves to modulate sounds to compose words or to coordinate movements to be able to walk, to use our sight to learn about unfamiliar objects or to play an instrument for years to become good musicians.
From all this, it is clear that odor perception is a complicated, subjective process shaped by a complex interaction of physiological, genetic, experiential, and cultural factors. As we have seen, the same molecule can evoke different sensations and interpretations among individuals. For these reasons, training the sense of smell should and can be done: it is a stimulating process that will lead to significant improvements over time.