A video uses lasers to show how you spit when you talk

April 21, 2020 Off By enlivenlabs

Even if you don’t think you spit when you talk, you definitely do — and a new video highlights that spit with lasers. The video, published in The New England Journal of Medicine, showed how the spurts of particles released when someone said “stay healthy” at various volumes. Then, it showed how the particle volume changed when the same person said “stay healthy” with their mouth covered by a damp washcloth.

The video, and other visualizations like it, are useful ways to understand that stuff flies out of your mouth all the time, not just when you cough or sneeze. Those respiratory emissions are one of the ways experts think the novel coronavirus spreads. But depending on how they’re made, these types of demonstrations can be misleading — and could give people a false sense of security.

Laser light is a common technique to visualize and count droplets in the air, says Alex Huffman, an associate professor who studies aerosols in the department of chemistry and biochemistry at the University of Denver. Huffman was not involved in the video, but he says this demonstration with the technique is a useful way to show that just talking can still send spit flying.

“You’re visualizing that qualitatively to say, I see stuff coming out of my mouth when I talk, and when I stick something in front of my face, less comes out,” he says.

That’s the goal behind the recommendation from the Centers for Disease Control and Prevention that everyone wear makeshift face coverings when they’re out in public. People can spread the novel coronavirus even when they don’t feel sick. If they pull something tight over their mouths, they might not emit as much virus when they talk or breathe — cutting down, even if just slightly, on the risk they’ll pass it to someone else.

Visualizations, though, are only as instructive as the parameters under which they’re made. The NEJM video’s laser only captured particles between 20 and 500 micrometers (the width of a human hair is around 75 micrometers). People also produce particles a lot smaller than that when they talk and breathe, and smaller particles can still carry microscopic bugs, including the novel coronavirus.