leungchopan/Shutterstock“God bless you!” What many of us say today as a folksy, knee-jerk response to any sneeze that enters our earshot was once a genuine precaution against eternal damnation. While plague ravaged the Mediterranean in the 4th century, Pope Gregory I decreed that every sneeze be greeted with a hearty blessing, as sneezing was the first sign a person was falling ill. Even earlier cultures worried that a sneeze was literally the soul being yo-yoed out of the body, leaving the sneezer temporarily prone to invasion by demons. An appeal to the lord was certainly in order.
Today we recognize sneezing for a sign of more practical dangers: the airborne spread of germs. And, while your soul may be safe, it seems our bodies are at even greater risk of contamination than previously suspected. Ongoing research from MIT shows that we’ve all been grossly underestimating just how far germs can travel in a single sneeze, and how long they can linger in the air afterward.
Lydia Bourouiba, a professor at MIT’s department of Civil and Environmental Engineering, leads a team that studies the nitty-gritty fluid dynamics of everyday expulsions, including sneezes, coughs, and even toilet bowl splashback. Her goal: to better understand how diseases spread, by capturing the exact moments when germs leave one person’s body and enter the open air. Using high-speed, black-and-white cameras able to record up to 1,000,000 frames per second, Bourouiba and her team recorded a string of volunteer sneezers under special lighting that accentuated moisture particles against a dark backdrop. To produce natural sneezes unpolluted by pollen nor pepper, Bourouiba resorted to a “universal method” of sneeze induction: nose tickling.
The resulting sneeze footage, which you can see in the below video of MIT’s findings, shows what Bourouiba calls a “turbulent cloud” of microbes that includes both large, solid droplets and moist, gaseous particles largely invisible to the naked eye. In a misty puff that looks something like a barfly exhaling smoke or a fire-breathing dragon spouting a gust of flame, large droplets arc to the ground while the smallest particles swirl and spread, helping carry airborne fluid invisibly across the room.
According to the team’s accompanying analysis, droplets from a single sneeze can travel up to 8 meters away — that’s 26 feet, the length of U-Haul’s largest available moving trucks—and linger in the air for up to 10 minutes, depending on environmental conditions. Scarier still, these migrating clouds of fluid tend to swirl upward toward the ceiling, where many public buildings install their ventilation systems. A single sneeze could easily spread contaminated droplets across a room, up though a ceiling duct, and into circulation through a building’s ventilation system.
“Gross,” you might think—and you’d be right. But this research is also vital to understanding the mechanics of airborne germ transmission, and the first step toward implementing new health and safety protocols to shield ourselves from it. Bourouiba believes her team’s research will lead to a refreshed conversation about how hospital ventilation systems are designed, and even how sick wards are organized to minimize contamination between patients during health emergencies.
In the meantime, you can do your part this allergy season by sneezing directly into a tissue (or your sleeve, in an emergency), carrying antibacterial wipes or gel to cleanse your hands, trying these natural allergy relief remedies, and—if you’re the superstitious sort—being quick to supply the poor snuffler on the bench next to you a kindly, “God bless you.”