Here's How Far a Sneeze Can Actually Travel
Respiratory droplets from a sneeze or a cough travel farther and linger longer than you might think.
Life during the coronavirus pandemic can be stressful, especially when you need to leave the house and be around other people—whether to get groceries or go into work. Even if you're following all the CDC guidelines, there are still so many unknowns, and every day we seem to learn more about protecting ourselves from COVID. A recent study may cast further doubt on our notions of personal safety by revealing how far viral particles from a sneeze or a cough can actually travel.
The University of California San Diego (UCSD) Jacobs School of Engineering study, published June 30 in the journal Physics of Fluids, found that respiratory droplets from a sneeze or cough traveled farther and lasted longer in climates that were cooler and more humid. In certain weather conditions, droplets could travel as far as eight to 13 feet away—even without wind. And because we know that person-to-person transmission through infected respiratory droplets is the most common cause of coronavirus infection, that's bad news for anyone who thinks keeping six feet away from someone is enough.
Previous studies have shown that social distancing can go a long way toward slowing the spread of coronavirus. The same is true of wearing a mask, which in this case, would greatly reduce the risk of being infected from distant viral droplets. As a UCSD write-up of the study notes, it's without masks that "six feet of social distance may not be enough to keep one person's exhalated particles from reaching someone else."
This isn't the first time the "six feet apart" rule has been called into question by a study on how far sneezes and coughs can actually travel. A May study in Physics of Fluids came to a similar conclusion that six feet was not enough when focused on the impact of wind on respiratory droplets. That study found that in breezier weather, droplets could travel up to 20 feet in five seconds.
Of course, it's not just how far these droplets travel—but also how long they linger in the air. Scientists now believe that airborne COVID particles are infectious, which means you may not even need to be near a person when they sneeze to inhale their respiratory droplets and become sick. That is, depending on the temperature and humidity.
"Droplet physics are significantly dependent on weather," study co-author Abhishek Saha, a professor of mechanical engineering at the UCSD, said in a statement. "If you're in a colder, humid climate, droplets from a sneeze or cough are going to last longer and spread farther than if you're in a hot dry climate, where they'll get evaporated faster."
While small droplets evaporate quickly and large droplets fall to the ground fast, it's droplets in the middle that are the biggest cause for concern, according to researchers: These sneezed or coughed droplets travel the farthest and take the longest time to disappear. As the study write-up notes, that's all the more reason to wear a mask, "which would trap particles in this critical range"—no matter what the weather is like. And for more on face coverings, You Should Not Be Wearing One of These Instead of a Face Mask, CDC Warns.