Is it possible to smell fear

Humans can smell fear and disgust, and the emotions are contagious, according to a new study. The findings, published Nov. Most animals communicate using smell, but because humans lack the same odor-sensing organs, scientists thought we had long ago lost our ability to smell fear or other emotions. To find out, the team collected sweat from under the armpits of 10 men while they watched either frightening scenes from the horror movie "The Shining" or repulsive clips of MTV's "Jackass.

Next, the researchers asked 36 women to take a visual test while they unknowingly inhaled the scent of men's sweat. When women sniffed "fear sweat," they opened their eyes wide in a scared expression, while those smelling sweat from disgusted men scrunched their faces into a repulsed grimace.

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.

In a conference presentation last year, Mujica-Parodi wrote : "We demonstrate here the first direct evidence for a human alarm pheromone … Our findings indicate that there may be a hidden biological component to human social dynamics, in which emotional stress is, quite literally, 'contagious'.

Simon Wessely, a psychiatrist at the King Centre for Military Health Research at King's College London told New Scientist that the idea that a fear pheromone could be developed as a chemical weapon is scientifically implausible. He said that a purely physiological cue is not enough to induce fear if people are not in a frightening situation.

The findings will be controversial because most researchers do not believe that humans can detect pheromones. In other mammals, this is done using a structure in the nose called the vomeronasal organ. Although humans have one of these it is not connected to the brain. However, human pheromones could still be detected elsewhere and some small studies have suggested that human behaviour can be modified by an alarm pheromone.

In one study in , for example, 60 women were asked to distinguish between sweat pads worn by women who had watched the horror film Candyman or a documentary.