New research highlights why you should close the lid every time you flush a toilet. A new study reveals how toilet water spray sends potentially dangerous germs into the air at alarming rates. Scientists from the University of Colorado in Boulder performed several experiments that uncovered an “invisible plume” that shoots into the air every time a toilet is flushed. The spray contained microscopic particles of pee, poop and whatever else was in the bowl. This creates a health hazard for those who follow.

According to Study Finds, the research team used bright green lasers and cameras to reveal how these particles are rapidly ejected from a lidless public toilet.

“If it’s something you can’t see, it’s easy to pretend it doesn’t exist,” said lead author John Crimaldi, a professor of civil, environmental, and architectural engineering in a University of Colorado statement. “By making dramatic visual images of this process, our study can play an important role in public health messaging.”

Researchers have known for decades that when a toilet is flushed, solids and liquids go down as designed, and tiny, invisible particles are released into the air. Previous studies have used scientific instruments to detect these airborne particles and shown how larger ones can land on surrounding surfaces, but this is the first glimpse of what the germy toilet plumes look like and how far they go.

Experts say that understanding the trajectories and velocities of these particles — which can transport pathogens such as E. coli, C. difficile, noroviruses and adenoviruses – is important for mitigating exposure risk through disinfection and ventilation strategies, or improved toilet and flush design. The virus that causes COVID-19 is present in human waste, which made experts recommend that people wear masks when using public toilets during the pandemic.

According to the New York Post, a study conducted by the Association for Professionals in Infection Control and Epidemiology found that the virus can be propelled into the air through a toilet plume after a flush.

“Close the lid and then flush,” Qingyan Chen, a mechanical engineering professor from Purdue University told Forbes. He said it was a simple solution to help control the spread of disease through toilet plumes. Chen said that closing the lid can prevent 80% of fecal particles from escaping into the air.

The CU Boulder scientists found that these airborne particles shoot up quickly, at speeds of 6.6 feet per second, reaching 4.9 feet above the toilet within 8 seconds. While the largest droplets tend to settle onto surfaces within seconds, the small particles that are less than 5 microns can remain suspended in the air for minutes or longer.

According to the statement by researchers, it’s not only their own waste people have to worry about. Many other studies have shown that pathogens can persist in the bowl for dozens of flushes, increasing potential exposure risk.

Crimaldi says his research team also measured the airborne particles with an optical particle counter, a device that sucks a sample of air into a small tube and shines a light on it to measure and count the particles. The team found that smaller particles not only float in the air longer, but they are also more readily absorbed into the nose and lungs, making them more hazardous to human health.

Hopefully, the study results will lead to more sanitary improvements in plumbing design, disinfection, and ventilation strategies to reduce the risk of exposure to pathogens in public restrooms.