You know the foods you eat affect the makeup of your body, but what about the things you watch? A team of German scientists say that the chemistry of moviegoers’ breath changes during funny or suspenseful scenes. The researchers published their findings in the journal Scientific Reports.

We’re constantly exchanging molecules with the world around us. We take in bacteria from the buildings we occupy, and each of us travels in a cloud of our own signature blend of microbes. We’re also expelling gas constantly, and not just through our butts. Our skin and breath contain all kinds of chemical compounds. In recent years, scientists have begun to appreciate our effusions as diagnostic tools. Your breath can tell a doctor if your blood sugar is high, or if you have a bacterial overgrowth in your gut. It can tell a police officer if you’ve been drinking. And now, it seems, breath chemistry could be a pretty good indicator of certain emotions. 

Jonathan Williams is an atmospheric chemist at the Max Planck Institute for Chemistry. He’s especially interested in the combined exhalations of large groups of people, and has previously studied the breath of sports fans at a local stadium. For this study at the cinema, Williams said in a press statement, “We were wondering whether it is possible to chemically differentiate between scenes in which different emotions are induced." 

Williams and his colleagues conducted their experiment behind the scenes in a large cinema complex. They set up their instruments in a utility room and plugged into the vents, which pumped out circulated air from inside the theater. The equipment captured and analyzed air from hundreds of viewers during screenings of Dinosaurs 3D, Buddy, and The Hunger Games: Catching Fire. 

Co-author Thomas Kluepfel, collecting moviegoers' breath in a not-creepy way. Image Credit: MPI for Chemistry

The researchers watched all three films and gave each scene an emotional category, like “mystery,” “comedy,” “romance,” “chase,” or “suspense.” They then matched the timeline of the movie to the flow of breath passing through the air vent in order to figure out when people were exhaling what. 

They found that yes, it is possible to spot different emotions in exhaled breath, but some were clearer than others. “We got a clear chemical signal for humorous and suspenseful scenes,” said co-author Jörg Wicker, “and were able to identify these even without seeing the movie.” The authors suggest that suspense and comedy might elicit stronger chemical responses because “these could be interpreted as an evolutionarily advantageous alert/stand-down signal, if perceivable by others.” In other words, your breath that smells like "ha-ha funny" could be an unconscious signal to those around you that it’s okay to relax. 

Of all three movies, the action-packed, super-suspenseful Catching Fire produced the most dramatic results. "The chemical signature of 'The Hunger Games' was very clear; even when we repeated the measurements with different audiences," Williams said. "The carbon dioxide and isoprene levels in the air always increased significantly as the heroine began fighting for her life." We were rooting for you with every breath, Katniss.