What if a product’s success is influenced not only by the aromas we smell, but also by the aromas we don’t smell?
We spend enormous amounts of time refining what we can consciously perceive. We adjust top notes, balance body, soften bitterness and obsess over descriptive language from sensory panels. Subsequently, in both fragrance and flavor, optimization often centers on what we can explicitly detect, describe and report back.
Subthreshold odors function like cinematic lighting ... remove it and everything suddenly feels flat, artificial or simply uninspiring.
However, research suggests that odors below the threshold of conscious detection can still shape perception, influence behavior and alter emotional responses. They may not appear in consumer vocabulary, and they are self-evidently tricky to measure, yet they can influence how products are experienced and valued.
In many ways, subthreshold odors function like cinematic lighting. Most people will be entirely oblivious to the on-set lighting design, but remove it and everything suddenly feels flat, artificial or simply uninspiring. My point is that we may be overlooking a powerful driver of product experience because, quite understandably, we focus on what we can consciously smell, as opposed to what we cannot.
Odor Thresholds are Not What We Think
Perhaps the most compelling demonstration comes from research by Thomas Hummel and colleaguesa. The researchers wanted to understand whether ingredients below conscious detection thresholds could still influence how the brain processes odor mixtures.
They screened 58 participants for sensitivity to Ambroxan (originally trademarked by Kao) and selected two groups: people who were highly sensitive to it and people who were effectively anosmic to it, despite both groups having otherwise normal olfactory function.
Participants were exposed to four conditions:
- Ambroxan alone
- a six-component mixture
- the same mixture with Ambroxan added
- an odorless control
Here’s where it becomes commercially interesting.
When participants were asked to distinguish the six-component mixture from the same mixture containing Ambroxan, both groups performed at chance. No one could reliably tell which mixture contained the Ambroxan. From a traditional sensory perspective, Ambroxan appeared functionally invisible.
Even though the participants couldn’t consciously detect the target odor, their brains still responded to it.
Yet their brains told a different story.
When fMRI was used to monitor neural activity during smelling, the participants who were sensitive to Ambroxan showed stronger activation in the insula, cingulate cortex and parahippocampal regions compared with insensitive participants. But more importantly, when Ambroxan was added to the six-component mixture, both groups showed altered neural responses despite being unable to consciously identify the difference.
Even participants who were effectively anosmic to Ambroxan showed increased activity in the right cingulate cortex when it was present in the mixture, implying that on a nonconscious level detection of Ambroxan occurred. Put simply, even though the participants couldn’t consciously detect the target odor, their brains still responded to it. But this phenomenon is not limited to olfaction.
Flavor is Constructed Before Awareness Catches Up
Research by Pamela Dalton and colleagues demonstrated that flavor perception can emerge from sensory signals that are individually undetectableb. Participants were exposed to subthreshold levels of benzaldehyde alongside subthreshold saccharin. Individually, neither the olfactory stimulus nor the taste stimulus could be consciously detected.
However, when presented together, participants became 28% more sensitive to benzaldehyde.
That effect disappeared when benzaldehyde was paired with water or MSG, suggesting that the brain was not simply combining weak signals. Rather, it responded specifically to combinations that were congruent, i.e., they aligned with prior experience. Sweetness and cherry-like aromas are commonly encountered together, and the brain appeared to use that learned association to construct flavor before conscious awareness fully engaged.
Sometimes subtle cues do disproportionate work. But what happens when we look beyond consumables and fragrances?
Anne Labbé and researchers at the Nestlé Research Center presented similar implications from their researchc. They found that subthreshold levels of the odorant ethyl butyrate increased perceived sweetness in sucrose solutions even when participants could not consciously detect the aroma. Interestingly, maltol did not produce the same effect despite also being associated with sweetness.
Even more revealing, increasing ethyl butyrate concentration did not proportionally increase sweetness perception. The effect behaved more like an on-off switch as opposed to a volume dial. This challenges the logical assumption that higher concentrations equal greater intensity. Sometimes subtle cues do disproportionate work. But what happens when we look beyond consumables and fragrances?
The Brain Secretly Scans One’s Odor Environment
Evidence suggests we are continuously scanning our environments for odors without conscious awareness.
Research from Noam Sobel and colleagues found that individuals with normal olfactory function performed approximately 240 additional exploratory inhalations per waking hour compared with anosmicsd. This suggests that every 15 seconds we are having a sniff to check for important odors without ever being aware of it. Interestingly, the rate decreased in an odor-free environment, suggesting an active process as opposed to an autonomic one.
Furthermore, research by Adele Mujica-Parodi found that smelling stress-related pheromone signals released by humans can trigger stress responses in others. This is despite such pheromones having no identifiable odore. Hence, we can begin to understand how odors which are for all intents and purposes undetectable, still have a direct effect on one’s emotional response.
The Most Powerful Aroma May Be the One You Never Smell
The implications are profound. While descriptive analysis centers around consciously identifiable product attributes, commercial success may also rely on components that fall below detection thresholds. Therefore, it’s not only the aromas we smell that are important, but also the aromas we don’t smell (so to speak).
In addition, the sensitivity of the human nose is commonly measured by conscious detection thresholds. But as it would seem, the nonconscious mind detects far more than thresholds would suggest. The intimation, therefore, is that one’s olfactory apparatus is more sensitive than we are led to believe. Such conclusions naturally introduce a pertinent question.
Sometimes the most powerful ingredient in a formula is the one nobody notices until it’s missing.
If subthreshold odors can alter neural activity, shape sweetness perception, influence emotional states and continuously inform how we scan our environments, are our current development frameworks overly reliant on what we can consciously articulate?
Certainly, at The Sensory Advantage*, my approach is to broaden the lens through which we predict a product’s commercial success. Acknowledging the potential of subthreshold odors is a significant layer within this framework because it goes both ways. Such seemingly innocuous components can certainly elevate a product, but they have the potential to tarnish it too. As you will no doubt intuitively understand, sometimes the most powerful ingredient in a formula is the one nobody notices until it’s missing.
References
aThomas Hummel et al. Brain responses to odor mixtures with subthreshold components. Behavioural Brain Research. 2013.
bPamela Dalton, Doolittle N, Nagata H, Breslin PAS. The merging of the senses: integration of subthreshold taste and smell. Nature Neuroscience. 2000.
cAnne Labbé et al. Subthreshold olfactory stimulation can enhance sweetness. Chemical Senses. 2006.
dNoam Sobel et al. Study on exploratory sniffing behaviour and olfactory sampling.
eAdele Mujica-Parodi et al. Chemosensory cues to conspecific emotional stress activate amygdala in humans. PLoS ONE. 2009.
*The Sensory Advantage is a sensory perception strategic consultancy that applies multisensory and predictive brain science to help food, beverage, and fragrance brands design, communicate, and optimize flavor experiences across product, packaging, and hospitality touchpoints.
