Emotions Seem to Be Detectable in Air

The chemistry in movie theaters changes during certain scenes—and it may be a subtle mode of communication.

Mario Anzuoni / Reuters

One of the most writerly things a person can do is to characterize air as thick, or emotions as tangible. Sadness lingers in the air. The best dinner parties are powered by palpable tension. The practice suggests that you are keenly attuned to your surroundings. Beyond observant, you use your senses in ways others had not thought possible. That is why people want to have sex with writers.

But if you told me that the air is actually transmitting chemical signals that influence emotions between humans, I would add you to a list that I keep in my head. It’s not a bad list, per se, but it is titled “Chumps.”

One person who would not be on that list is Jonathan Williams. An atmospheric chemist, he describes himself as “one of those wandering scientific souls,” but not in an annoying way. He maintains a jovial British lilt after moving to Colorado to work at the National Oceanic and Atmospheric Administration, and then to Germany for a job with the Max Planck Institute (which describes itself as “Germany’s most successful research organization”). There Williams and his colleagues study air.

They focus on gases that come from vegetation in the tropics, as well as carbon industry. In doing so, the chemists use finely calibrated machines that sense the slightest changes in the contents of air. Taking measurements in the field, Williams and his colleagues always noticed that when they themselves got too close to the machines, everything went haywire.

That made sense, in that humans are bags of gas. As breathing people know, we tend to emit carbon dioxide. (Though each exhalation still contains about four times as much oxygen as carbon dioxide.) And there are many subtler ingredients in the concoctions we breathe out. So Williams began to wonder, are these gases “significant on a global scale”? Could they be, even, contributing to climate change? Especially as the number of humans on Earth rockets toward 8 billion?

The answer was no. Just a clear, simple no. By measuring gases in soccer stadiums, the Planck chemists found no consequence of human breath. There might be some effect at a global scale, but it’s just nothing compared to the air-ravaging effects of transportation and agriculture.

But Williams didn’t come away from the stadium empty handed. As he sat and watched the fluctuating readings on the air sensors, he got an idea. In the manner of a typical European soccer crowd, the people went through fits of elation and anger,  joy and sorrow. So Williams began to wonder, as he later put it to me, “Do people emit gases as a function of their emotions?”

If we do, it wouldn’t be unprecedented. Tear some leaves off of a tree, for example, and it will emit chemical signals that may be part of a system of communication between trees. The behavior for bees and ants is clearly chemically dominated.

“We’re not like that—not like robots following chemicals,” Williams explained. “But it could be possible that we are influenced by chemicals emitted by other humans.”

The idea of airborne pheromones—chemicals that specifically influence mating behaviors— has been a source of much fascination, but the actual evidence is weak. Some small studies have suggested an effect when people put cotton balls under their armpits, and then other people smell the balls—but in minor, unreliable ways.

“I don't know why so many previous researchers have been so into armpits,” said Williams. “A much better way to communicate would be through your breath. Because you can direct your breath, and your breath is at roughly the same height as the person you’re trying to communicate to, silently. In the dark, maybe, in your cave.” And if these behavior-modifying volatile chemicals exist (volatile meaning anything that goes into the air), then why would they be limited to sex? Why shouldn’t we be able to signal fear or anxiety? It is true that birds seem to know that I'm afraid of them.

Williams was so intrigued by the idea of gases and emotion that he designed another experiment—something more predictable than a German soccer game. This time he used a movie theater. Unlike the open-air stadium, the theater presented fewer variables. “You’ve got this box, the cinema, and you spool through air from outside at a continuous rate, and you have 250 people sitting there, not moving. And you show them all, simultaneously, something that should make them frightened or anxious or sad, or whatever.”

The changes in any one person’s breath might be minuscule, but a crowd of breathers could be enough to overcome the rest of the background signals. And more importantly, unlike a soccer match, the experiment could be done with the same film again and again. This could test the reproducibility of findings, which is critical to science.

Rigging a mass spectrometer into the outflow vent of the theater, the Kino Cinestar in Mainz, Williams had a sense that the experiment as something of a lark. “I thought, we’re probably just going to get a big mixture of popcorn and perfume,” he said. But, nonetheless, to measure relationships between scenes and gases, his team meticulously mapped out and labeled every scene in 16 films—from beginning to end. In 30 second increments, the team labeled each by its quality (kiss, pet, injury), as well as its emotional elements using a finite set of descriptors.

Their efforts were not entirely wasted. They published the findings this month in Scientific Reports, an open-access journal published by Nature. After measuring more than 100 chemicals in the theater air from 9500 filmgoers, the team saw some changes that stood out—at the same points, in almost every showing of some films.

In Hunger Games: Catching Fire, for example, during the “suspense” scenes—when Jennifer Lawrence was in particular danger—the carbon dioxide, acetone, and isoprene levels in the theater air predictably increased. The researchers speculate that this may have something to do with breath-holding, or stress hormone production—but it is all speculation. The important point was that the signals occurred at exactly the same time in all four screenings of the film. They also found the reproducible changes in the air chemistry during “humor” scenes in other films.

It’s impossible to say whether the changes in the air are signals to one another, or simply byproducts of emotion-based reactions. To Williams, that’s “the billion-dollar question.” But he is guarded in his excitement. “We have shown there is this invisible, inaudible concert of chemicals that changes regularly in the auditorium. We haven't shown that people can detect them. But, of course, if a signal is there, then maybe it does.”

“The authors do make a very important point about the effects of stress or anxiety on human emissions,” said Ben De Lacy Costello, a senior research fellow at the University of West England. He created a catalog of all the chemicals we emit and found at least 1840 . Though it was published in The Journal of Breath Research, the list included volatile organic compounds (VOCs) coming from many parts of healthy people: 359 in saliva, 154 in blood, 256 in breast milk, 532 in skin secretions, 279 in urine, and 381 in feces—in addition to 872 in our breath.

Williams and Costello, among others who study air and perception, refer to the volatile chemicals we humans emit as the volatolome. It’s a linguistic construction akin to our genes collectively being called our genome, and our microbes making up our microbiome.

Interesting as movie theaters and pheromones might be, VOCs are potentially useful in innumerable practical ways. A 2016 study found that the breath volatolome might be helpful in making the critical medical diagnosis of pulmonary-arterial hypertension. And some dogs have proven capable of smelling certain cancers—presumably because the metabolically altered tumor cells produce unique byproducts. Based on that, entrepreneurs have attempted to create artificial “cancer-sniffing” noses.

Costello believes that once fully understood (if it ever is), the number of chemicals in the volatolome may be in the tens of thousands. Many will come, like the smells in our armpits and on our breath, from the huge range of microflora on and in the human body. The possibilities for disease screening and detection are enormous.

Among healthy people, it might be possible to measure these gases to track other bodily changes not just in diseases, but normal responses to food and exercise and stress. As Costello posits, “It could be useful to detect stress, for example, in rescue situations such as earthquakes, monitoring crowds of people, terrorists in airports, et cetera.”

Media, too, change our moods by changing the chemistry inside us, and so changing the chemistry we emit. Humans are notoriously unreliable when it comes to research that requires introspective self-report, but your gases won’t lie. Though we’re far from it now, some day when that special person tries to tell you that the two of you just don’t have chemistry, you might be able to refute that with data.