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Sneeze Scientist

Lydia Bourouiba examines how snot droplets in sneezes help spread disease

Lydia Bourouiba has recorded more than 100 sneezes and coughs. She watches the videos in slow motion to learn how these actions produce droplets of mucus that can fly through the air. Bourouiba is a mathematical physicist at the Massachusetts Institute of Technology who studies how fluids move. She’s also one of the world’s leading sneeze and cough experts. 

Sneezing is the body’s way of expelling unwanted particles, like dust or germs. It can also spread disease. If another person touches or inhales infected droplets sprayed by a sneeze, he or she can get sick. Bourouiba hopes that  her research will help public-health experts stop epidemics. An epidemic is the rapid and widespread outbreak of a disease. She spoke with Science World about her job investigating how sneezes travel. 

What causes a sneeze?

Sometimes when a person breathes in, his or her nose or trachea, a tube that carries air from the lungs to the throat, becomes irritated. A sneeze is a type of reflex, or automatic response, to that irritation. It occurs when a person quickly inhales to fill his or her lungs. Then a fast-moving, turbulent cloud of hot, moist air is expelled from the mouth. The cloud is full of droplets that can carry germs. How and why do you record people sneezing? To trigger a sneeze, we use a special device to tickle the inside of a volunteer’s nostrils. Suddenly- ACHOOO! The person sneezes, sending a spray of snot through the air. A lot of these droplets are so small, and travel so fast, that you can’t see them with the naked eye. By capturing them on video, we can slow down the process and zoom in on the details. We use different types of lighting when recording so we can see the larger droplets as well as the cloud of tinier particles that make up a sneeze. Some types of lighting can make the particles look white, so we can view how this cloud moves. How does this help you study diseases? We track the sneeze cloud and its trajectory, or path through the air. This helps us understand how germs spread. We look at how the droplets form, how quickly and where they settle, or how long the cloud carries the particles in the air. The more elastic mucus is, the longer it can stretch before breaking into droplets. We use mathematics and physics to create equations based on data collected from our videos. These equations predict what happens to a sneeze or a cough cloud. They also factor in how conditions like temperature and moisture can influence how a sneeze contaminates a room or even a whole building.  What prompted you to start studying sneezes? I was trained in mathematics and physics but was also interested in health. We still have a lot to learn about how illnesses spread from one person to another. Do they spread differently depending on the type of room we are in? Does people’s distance from an infected person affect whether they also get sick? We simply do not know. I started trying to find some answers to these questions. If we can stop the spread of disease from one person to another, we could potentially stop an epidemic. What are you working on right now? So far, my team and I have focused on healthy patients. We are about to start recording individuals with cold and flu symptoms. We will examine how their exhaled particle clouds might differ from those of healthy people.  What can be done to stop epidemics? Once we know more about how illnesses spread, we can advise health-care facilities on how to best contain or prevent the spread of germs. For example, they might change their guidelines on how long people should wait before entering a room that an infectious person was in. They might also work to improve ventilation—the movement of fresh air into a room. Airplanes, schools, and other crowded or confined locations might also benefit from these changes. 

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