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.”
Scientists at Rice University used a different approach to test whether or not humans could in fact smell fear by monitoring responses to images rather than brain scans. They collected sweat from a group of men while they watched the parts of horror movies considered to be scary. They then asked a group of women to view pictures of facial expressions that were ambiguous, or in other words, not clearly happy or fearful.
The women were more likely to label the ambiguous expressions as fearful when they were smelling the horror-movie induced sweat. The smellers did not, however, see fear in faces that were unambiguously happy no matter what they were smelling. The authors on the study suggest that the additional olfactory information can help us draw conclusions when the information we gather from our more dominant senses like sight is incomplete.
Is fear contagious?
Another study published in the journal of Psychological Science and led by scientists at the University of Utrecht took the study of the smell of fear one step further and explored whether or not we actually feel fearful when we smell fear. The Dutch scientists collected sweat from a group of men as they watched clips from the horror movie "The Shining" and while they watched gross scenes from the slapstick-type MTV show called "Jackass." They then subjected a group of women to smelling the different kinds of sweat while giving them a visual sorting task like locating a specific object in a crowded image.
These studies appear to contradict the idea that we communicate as humans only through language and visual cues.
The researchers then monitored the facial expressions of the women as they performed their otherwise emotion-free visual tasks. The women showed a clear tendency for making fearful expressions (like wide eyes) while smelling the horror-inspired sweat and for scrunching up their faces in disgust while smelling the sweat produced while witnessing gross scenes.
Thus, not only do our brains process signals from fear-induced (and possibly disgust-induced) sweat differently, but our brains may also absorb some of that emotion. The authors of the Dutch study claim that their “research suggests that emotional chemo-signals can be potential contributors to emotional contagion in situations involving dense crowds”
While still somewhat circumstantial, these studies do appear to contradict the idea that we communicate as humans only through language and visual cues. However, there is still much to learn about the smell of fear as scientists, for example, have not yet been able to identify a specific chemical that can be clearly linked to fear and its potential odor. But if you don’t want your friends to sense that you’re afraid at that haunted house this Halloween, perhaps you should layer on the deodorant extra thick.
Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.
Image courtesy of shutterstock.
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