Sneezes and coughs project germs farther than previously thought

Each time you cough or sneeze, you may be sending a mini cold front across the room -- a germ-filled weather system. According to a new study by researchers at MIT, the liquid droplets and vapors expelled during a cough or sneeze can float for up to eight feet. Scientists had previously assumed mucus could only fly a couple of feet, and that larger droplets always traveled farthest given their greater mass. This assumption would be correct if droplets were expelled one by one in a vacuum. But they're not. New analysis by MIT researchers shows the droplets and vapors of a sneeze or cough don't exist in isolation, but interact with each other and the air around them. They act more like a "multiphase turbulent buoyant cloud," as the researchers write in their paper. "The cloud entrains ambient air into it and continues to grow and mix," explained co-author Lydia Bourouiba, an assistant professor in MIT's Department of Civil and Environmental Engineering. "But as the cloud grows, it slows down, and so is less able to suspend the droplets within it. You thus cannot model this as isolated droplets moving ballistically." Using high-speed imaging, lab simulations and mathematical modeling, researchers were able to show how the smallest sneeze and cough droplets often down dissipate from the cloud until after they've floated eight feet -- or halfway across the room. The end goal for these researchers is to better understand how pathogens spread, specifically among populations indoors. As of now, the best remedy to slow the germ cloud is putting your elbow up to your face to block the expulsion. The details of the sneeze study were published this week in the Journal of Fluid Mechanics.