60-Second Health

Snot Clouds Achieve Unexpected Buoyancy

Sneeze and cough particles form a cloud whose turbulence pulls in surrounding air, which allows the goop to maintain buoyancy and move farther than expected. Cynthia Graber reports

Gordon: “When you have to sneeze or cough, do it into the bend of your arm.”
Elmo: “Sneeze into your arm with Elmo. Ah-choo!”

Gordon and Elmo from Sesame Street are right. And M.I.T. researchers recently found that viruses can travel much further than we thought. Which shows how important it is to block coughs and sneezes.

The researchers used high-speed imaging of folks coughing and sneezing, along with simulations and mathematical models. The new research shows that multiple drops travel in a cloud. And the cloud’s turbulence pulls in surrounding air, which allows the goopy assemblage to maintain buoyancy and move farther.

Heavier particles drop out first, but about five times farther out than had been previously predicted. And the small ones swirl around and can be carried 200 times past previously predicted distances. The research is in the Journal of Fluid Mechanics. [Lydia Bourouiba, Eline Dehandschoewercker and John W. M. Bush, Violent expiratory events: on coughing and sneezing]

Longer flight distances means coughs and sneezes can often reach ventilation systems. The researchers thus encourage hospital and airplane engineers to consider designs that block droplet flight and thus keep everyone else from catching your cold.

—Cynthia Graber

[The above text is a transcript of this podcast.] 

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