By Adam Hadhazy, Office of Engineering Communications
For the first time, researchers have directly visualized how speaking produces and expels droplets of saliva into the air. The smallest droplets can be inhaled by other people and are a primary way that respiratory infections like COVID-19 spread from person to person.
Using high-speed imaging, the researchers showed that when our mouths open to produce speech sounds, a film of lubricating saliva initially spreads across the lips. As the lips part, the liquid film then breaks into filaments. Outward airflow from the lungs stretches and thins the filaments until they eventually rupture and disperse into the air as miniscule droplets — all within fractions of a second.
This droplet-producing mechanism is especially pronounced for so-called stop-consonants or “plosives” like “p” and “b,” which require the lips to firmly press together when forming the vocalized sound. Other sounds known as denti-alveolar plosives, such as “t” and “d” which involve the tongue touching the upper teeth and the jaw ridge just behind the teeth, likewise produce droplets at a much greater rate than when forming vowel sounds.
A deeper understanding of this droplet formation and dispersal process should lead to new and better mitigation strategies, helping to slow down the current coronavirus pandemic along with future outbreaks.