Haunted houses, scary movies and spooky sights abound this time of year. Fear is in the air. Can you smell it? While that may sound like a ridiculous prospect, it's not. Science says so.
You may have heard that some animals, such as bees and dogs, can smell fear. That statement is somewhat true and somewhat misleading, according to Penn State University. Fear itself does not have a scent, but the pheromones produced when an animal is afraid do.
Pheromones are chemicals emitted by all animals in bodily fluids, such as sweat and urine, that send signals to other animals of the same species. They may indicate territory, aggression or an interest in reproduction. But we don't smell these scents in the same way we would smell a fresh-baked apple pie or a fire burning in the fireplace. We detect those through our main olfactory system, but pheromones are registered through our accessory olfactory systems. PSU explains:
Communication in this system begins in the vomeronasal organ, which is located above the soft palate of the mouth, on the floor of the nasal cavity. Highly specific smell molecules detected by this organ are transmitted to the accessory olfactory bulb where they are collected and processed. Nerves from both the accessory and the main olfactory bulbs project to the limbic system, the part of the brain that deals with emotional perception and response.
PSU also points out that smells are processed and interpreted in the limbic system, and there, an organ called the amygdala is responsible for perceiving and responding to fear. So it makes sense that an animal would be able to "smell fear."
While some scientists question whether human pheromones really exist, others point to studies like this one from 2012, which found that humans can indeed communicate emotional states via chemical signals.
Fear as a social contagion
Not only can we communicate fear, but the feeling of fear is contagious, a study published in 2009 found. To determine this, a team of researchers taped absorbent pads in the armpits of 20 people about to skydive for the first time. As they perspired, the pads soaked up the sweat before and during the jump. As a comparison, the scientists also collected sweat samples from the same 20 people (11 men and nine women) while they ran on a treadmill.
The team then asked two groups of volunteers to sniff the sweat (file that under jobs I'd never want). One group got the fear sweat, and the other the treadmill sweat. As the volunteers did their dirty work, a brain scanner monitored their response. It showed the fear centers of the brain were activated when volunteers sniffed the skydive sweat even though the volunteers said they couldn't tell the difference between the samples.
In a conference presentation, study author Lilianne 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.'"
In another study, psychologist Denise Chen asked a group of volunteers to smell sweat from study participants who had watched a funny movie clip or a scary one. More than half of them correctly identified which sample was fear sweat even though they said they could not smell any difference. The study demonstrates "an immediate effect of airborne chemicals on human moods," according to the authors.
But don't let all this create the impression that humans are super-sniffers like dogs, elephants or rats. The authors of the 2009 study noted that behavior is another important factor in the emotion-contagion equation. In other words, people pick up on and imitate social behaviors, so if you see someone who is clearly frightened, you may become frightened as an instinctual reaction, not necessarily a chemical one.