No matter where you go, the movie theaters tend to smell the same: like popcorn, and the butter-like stuff they put on the popcorn, and that stale odor of recycled air-conditioned air.
Also fear, and sadness, and joy. These feelings aren’t scents, per se, in that you don’t take a whiff of air and consciously think, “Man, it smells scary in here.” But in a study published earlier this week in the journal Nature, a team of researchers found that the air in movie theaters tends to take on unique chemical signatures based on how the audience reacts to what’s happening on the screen. A horror film, for instance, will have a different chemical imprint than a comedy, which will leave a different mark than a tearjerker.
The researchers collected air samples from two theaters in a cinema in Mainz, Germany, over the course of six weeks, sorting each individual scenes from the movies screened into categories like “crying,” “romance,” and “everyday life.” They then tested the samples for various chemicals, looking for patterns between the mix in the air and the content of a given scene.
As the Discover blog Neuroskeptic explained, the chemicals tended to accumulate in the air over the course of the movie, a natural effect of keeping a bunch of people together in a closed space. But the increase wasn’t always a steady line: During screenings of The Hunger Games 2: Catching Fire, for instance, carbon dioxide and isoprene both ticked up during two especially tense moments — carbon dioxide because people’s breathing likely sped up, meaning they exhaled more gas, and isoprene, perhaps, because the tense scenes made them fidgety (isoprene, Neuroskeptic pointed out, is released during muscle movement).
As Neuroskeptic noted, the study’s analysis might be weakened by the sheer number of factors the authors examined: They collected data for more than a hundred different chemicals and dozens of movie scenes, meaning it may be hard to glean meaningful signals from so much noise. But given what we know about emotions and odors, the findings don’t feel all that surprising — our bodies are constantly giving off all kinds of chemical signals that clue others in to our state of mind. (In one 2009 study, for example, people who smelled sweat collected from skydivers were better able to identify threatening expressions from a lineup of faces, suggesting that an anxiety odor in the sweat may have primed them to be ready for danger.)
Maybe that movie-theater smell, in other words, isn’t just popcorn: It’s you and everyone else in the theater, feeling all your feelings together in the dark.
