Fear Factor

You’re watching a movie in a dark theatre. On-screen, a creature chases a teen through an eerie forest. Just when it seems like the boy is safe—a monster leaps from the shadows! You jump in fright, flinging popcorn everywhere.

Although the movie is rated PG-13, you feel like it might still give you nightmares. Rating movies isn’t an exact science. Labeling a film G, PG, PG-13, or R only provides a best guess as to its age appropriateness. But there could be a more scientific way to determine who should—or shouldn’t—be viewing a movie: chemicals in the air.

You’re watching a movie in a dark theater. On the screen, a creature chases a teen through a creepy forest. Finally, it seems like the boy is safe. Then a monster leaps from the shadows! You jump in fright, and your popcorn flies everywhere.

The movie is rated PG-13. But you feel like it might still give you nightmares. Rating movies isn’t an exact science. A film is labeled G, PG, PG-13, or R. That’s only a guess about what age groups it’s best for. But there could be a scientific way to decide who should or shouldn’t see a movie. The answer could come from chemicals in the air.

People’s bodies constantly emit compounds—substances made up of two or more chemically combined elements—through their skin and as they breathe. That fact got Jonathan Williams thinking. He’s an atmospheric chemist at the Max Planck Institute for Chemistry in Germany. He wondered whether the gases humans emit were significant enough to affect the world around us.

Williams took equipment that can detect chemicals in the air to a place with a lot of people: a soccer stadium. While he took measurements, he watched fans cheer in excitement and groan in disappointment as the match played out. Although the chemicals the crowd released collectively didn’t end up amounting to much, Williams’s observations did spark a new question: Do the gases people give off change depending on their mood?

To find out, Williams needed a place with fewer variables than a soccer stadium, whose environment was too big, open, and unpredictable. “Luckily, movie theaters are perfectly designed to test this,” says Williams. The audience sits in an enclosed space and simultaneously reacts to the same thing, so he could better control the factors that would influence his investigation.

People’s bodies constantly release compounds from our skin and breath. Compounds are substances made up of two or more chemically combined elements. That got Jonathan Williams thinking. He’s an atmospheric chemist at the Max Planck Institute for Chemistry in Germany. He wondered if the gases we release are strong enough to affect the world around us.

Williams used equipment that can detect airborne chemicals. He took it to a soccer stadium, a place with a lot of people. As the match played out, he took measurements. He watched fans cheer in excitement and groan in disappointment. All together, the chemicals the crowd released didn’t amount to much. But Williams’s test did raise a new question. Do the gases people give off change with their mood?

Williams wanted to find out. But he needed a place with fewer variables. A soccer stadium was too big, open, and hard to control. “Luckily, movie theaters are perfectly designed to test this,” says Williams. The audience sits in an enclosed space. They all react to the same thing at the same time. So Williams could better control the factors that would affect his study.  

At a local cinema, Williams’s team hooked up an instrument to the ventilation system that would sample the air every 30 seconds. They used the device to identify the airborne chemicals audience members’ bodies produced during 135 showings of 11 different movies.

The team then compared the chemicals detected with the film plots. Williams found that levels of isoprene spiked during suspenseful moments in movies (see Movie Chemistry). Muscles release this chemical whenever people tense up or move—for instance, if they become startled when scared.

It turned out that the data Williams collected was a good indicator of just how intense a film really is for different age groups. “You can almost [tell what’s going on in] the movie by looking at the variation of chemicals people emit,” he says.

At a local cinema, Williams’s team connected an instrument to the ventilation system. It would sample the air every 30 seconds. They used the instrument to identify the airborne chemicals from audience members’ bodies. They ran it during 135 showings of 11 different movies.

The team detected the chemicals and compared them with the film plots. Williams noticed something during suspenseful moments in movies. Levels of isoprene spiked (see Movie Chemistry). Muscles release this chemical when people tense up or move. For example, it’s released if they get scared and jump.

Williams’s data turned out to be a useful guide. It showed just how intense a film really is for different age groups. “You can almost [tell what’s going on in the movie] by looking at the variation of chemicals people emit,” he says.