WASHINGTON — A cough or sneeze in public isn’t nearly as innocuous as it once was. Now, a new study reports that COVID-19 can also spread from asymptomatic carriers simply speaking. Researchers in Japan say COVID carriers can spread the virus via small aerosol droplets in their exhaled breath while talking to someone else in close quarters.
The scientists often use lasers and smoke to study the flow of expelled air as two people converse across various service industry settings. For example, sitting in a barber’s chair getting a haircut, or sitting in a doctor’s office. For this research specifically, the team used electronic cigarettes to create artificial viral droplets. The liquid, a mixture of glycerin and propylene glycol, makes it very easy for scientists to track and visualize airflow patterns.
“We analyzed the characteristics of exhalation diffusion with and without a mask when a person was standing, sitting, facing down, or lying face up,” says study author Keiko Ishii in a release by the American Institute of Physics.
Researchers recorded the resulting vapor cloud over and over as participants repeated the common Japanese business greeting “onegaishimasu” while holding various relevant poses. The experiment took place in a local hair salon in Tokyo.
“A significant amount of similar face-to-face contact would occur not only in cosmetology but also in long-term and medical care,” Ishii adds.
Those experiments illustrated that exhaled air from an unmasked individual talking usually falls down due to gravity. So, if another person is underneath the speaker, as is the case during a haircut, the customer may become infected.
If the speaker is wearing a mask, the vapor cloud will often attach itself to the speaker’s body, flowing upward, because their body is warmer than the surrounding air. Even with a mask on, however, if the hair stylist is leaning over it’s possible for the aerosol cloud to detach from the speaker and fall onto the customer.
“The face shield promoted the rise of the exhaled breath,” Ishii concludes. “Hence, it is more effective to wear both a mask and a face shield when providing services to customers.”
The study is published in Physics of Fluids.