If “toilet plumes” aren’t already on your list of reasons to avoid public restrooms, well, scientists at University of Colorado Boulder are doing their best to change that. They used green lasers and basic cameras to reveal what sprays up when you flush a typical commercial toilet.

It’s no secret that toilets spray when flushed, propelling aerosolized bits of water, poo, and even viruses like covid-19 into the air. But new research makes this sobering reality abundantly visible. The paper, titled “Commercial toilets emit energetic and rapidly spreading aerosol plumes,” is published in Scientific Reports.

“People have known that toilets emit aerosols, but they haven’t been able to see them,” said John Grimaldi in a University of Colorado press release. Crimaldi is lead author on the paper and a professor of engineering at the university, where he runs the Ecological Fluid Dynamics Lab. “We show that this thing is a much more energetic and rapidly spreading plume than even the people who knew about this understood.”

Grimaldi and his collaborators used continuous and pulsed lasers to create a thin, vertical sheet of bright green light aimed at the toilet. This sheet was able to light up and reveal the aerosol spray in the aftermath of a flush.

Through their analysis, the researchers found that the “strong chaotic jet,” as they call it in their paper, can reach a height of nearly 5 feet (1.5 meters), with a peak velocity of 6.6 feet (2 meters) per second within 8 seconds after the flush is activated. Larger particles—defined by the team as 5 to 10 micrometers, or about the size of a red blood cell—will fall out of the vapor cloud more quickly than smaller particles, which can linger in the air and eventually settle on various bathroom surfaces, bringing viruses and bacteria with them.

“If it’s something you can’t see, it’s easy to pretend it doesn’t exist. But once you see these videos, you’re never going to think about a toilet flush the same way again,” said Crimaldi. “By making dramatic visual images of this process, our study can play an important role in public health messaging.”