We all know to cover our mouths when we sneeze or cough (right?!), but recent research shows that it might not do as much as we think to contain our germs. In fact, a new study in the Journal of Fluid Mechanics looked at exactly where all that stuff goes when it leaves our bodies. Spoiler alert: farther than you think.
Researchers at the Massachusetts Institute of Technology (MIT) looked at what happens after a violent respiratory event: a scary name for coughing or sneezing. They knew that the fluid droplets we expel in coughs and sneezes are a combination of sizes—ranging from 1 micrometer (take a millimeter and divide that by a thousand!) to 800-900 micrometers. "The idea was that we mostly transmit diseases through the larger droplets that fall on other people and surfaces," says study coauthor Lydia Bourouiba, Ph.D., assistant professor at MIT. They previously thought that those larger droplets were going to travel farther than the smaller ones—reaching about 1 meter while the smaller droplets stayed around 30-50cm in front of you. What they actually found was a lot more surprising!
They used high-speed imaging to track where the droplets actually went. It turns out, there's a crucial respiratory cloud that you expel every time you sneeze or cough, which is made up of hot/moist air and some water. This cloud actually enhanced the range of the smaller droplets, helping them travel way farther than they previously thought. The larger droplets traveled a tiny bit farther—still staying within two meters from the sneezer. However, the smaller droplets could reach the scale of a room (about 4 meters), and may travel even farther through ventilation.
So what does this mean? It's still helpful to sneeze into your hands or elbow to capture the larger droplets, but those smaller droplets may linger in the air long after you cough, says Bourouiba. But don't panic, these new findings just give researchers a better understanding of the patterns of transmission—it doesn't mean you need to evacuate a room every time someone coughs. Bourouiba still recommends washing your hands often and cleaning surfaces that may harbor germs, and obviously, make sure to cover your nose and mouth this allergy season!