A lot of things can cause a sneeze—from sickness to sex. But sneezing can be pretty gross. Sneezes eject particles of mucus and saliva, some contaminated with viruses and bacteria, at ten miles per hour, creating a giant cloud of potentially infectious mist. There's still much left to learn about how exactly that disgusting cloud moves. Most advice for avoiding sneeze clouds are largely educated guesses.
Mathematical physicist Lydia Bourouiba, head of the Fluid Dynamics of Disease Transmission Laboratory at MIT, has spent her academic career sussing out the secrets of the sneeze, reports Rae Ellen Bichell at NPR. Her most recent contribution to schnoz science is a slow motion video of sneezing, which she published at the New England Journal of Medicine.
The high contrast black and white video shows just how large a sneeze cloud can be. Understanding exactly where and how far vaporized mucus travels is important. “Respiratory infectious diseases still remain the leading infectious diseases in the world,” Bourouiba tells Bichell. “It's actually quite amazing that we can produce such a high-speed flow that contains all these ranges of sizes of droplets.”
Bourouiba’s analysis shows that just standing a few feet away from a sick patient doesn't remove them from the firing zone. Tiny droplets can hover in a room for several minutes and zip across an entire room in mere seconds.
In an earlier study, and a different set of sneeze videos, Bourouiba found that the droplets are are not uniform, contradicting previous guesses about sneeze spew. Instead, as the droplets exit the mouth and nose, complicated physics take hold. A combination of the sneeze force and turbulence causes the production of a range of particle sizes, from fine lingering mists to larger spray drops. And even tiny drops, Bourouiba found, can harbor disease causing agents.
Bourouiba says mapping the sneeze cloud could help hospitals and places facing epidemics figure out how to squelch the spread of diseases. Air temperature, humidity, room layout and ventilation could all be tweaked to reduce person-to-person transmissions. For example, when someone sneezes on a plane, the airflow patterns actually facilitate the spread of spray to nearby passengers. But not everyone is just sitting by with a cringe. Raymond Wang won the 2015 Intel Science and Engineering Fair for his innovative airflow foils for the plane interior which actually prevent the spread of germs in the enclosed space.
“This is a major blind spot when designing public health control and prevention policies, particularly when urgent measures are needed during epidemics or pandemics,” Bourouiba says in a press release. “Our long term goal is to change that.”