Scientists have not been able to identify a specific chemical that communicates fear. However, there have been a range of studies that suggest we can use smells to transfer information including whether or not we are afraid.
Before a recent job interview, a colleague suggested to me that I would do best to exude as much confidence as possible because hiring committees could smell fear. My daughter’s father and I used to similarly joke that she could smell our fear when we were trying to convince her to go to bed at night. We know smells can trigger our memories, sometimes more effectively than other senses, but can odors also communicate emotions like fear? What does fear even smell like?
Animals, like reptiles and amphibians, that communicate with each other via nonvisual cues like chemicals make use of what is called a vomeronasal organ, a chemical receptor near the nose. While humans also have this organ, its function remains an unsettled area of ongoing research. For example, a clear link has not yet been drawn between the organ and our brains which would be needed to process any related signals.
Similarly, scientists have not been able to identify a specific chemical that communicates fear. However, there have been a range of studies that suggest we can use smells to transfer information.
Does fear sweat smell different?
A team of scientists at Stony Brook University, including Dr Lilianne Mujica-Parodi, collected sweat on cotton pads in the armpits of 20 people as they went skydiving for the first time and during exercise. Another group of people then smelled the two different kinds of sweat via nebulizers while their brain activity was monitored via an fMRI.
More activity was noted in the amygdala and the hypothalamus, the regions of the brain associated with processing emotions, including our fight or flight response, when study participants smelled the skydiving sweat relative to the sweat produced during exercise. Thus, the authors of the study concluded that emotional stress was being communicated by a kind of chemosensory signaling while the physical stress was not.
In a similar study involving brain scans, psychologist Bettina Pause of the University of Dusseldorf in Germany and her team collected sweat from 49 students at two different times: during exercise and right before taking a graded oral exam. They then scanned the brains of a separate group of students again using an fMRI while they smelled the emotionally-inspired versus the physically-inspired sweat.
Those smelling the sweat did not claim to be aware that they were even smelling anything in at least half of the trials. Those that did notice an odor rated it as mild, a result that is consistent with the fact that any of us would be hard-pressed to describe what fear smells like.
However, their brain scans gave away a lot more information than their comments did. Just as in the sky diving study, the sweat produced leading up to the oral exam activated the part of the smeller’s brain linked to empathy and processing the emotions of other people. So even though the study participants did not think they could tell the difference between the different smell triggers, the study authors concluded that the olfactory system was effective at processing “emotional contagion.”