The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission

Proc Natl Acad Sci U S A. 2020 Jun 2;117(22):11875-11877. doi: 10.1073/pnas.2006874117. Epub 2020 May 13.


Speech droplets generated by asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are increasingly considered to be a likely mode of disease transmission. Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per second. In a closed, stagnant air environment, they disappear from the window of view with time constants in the range of 8 to 14 min, which corresponds to droplet nuclei of ca. 4 μm diameter, or 12- to 21-μm droplets prior to dehydration. These observations confirm that there is a substantial probability that normal speaking causes airborne virus transmission in confined environments.

Keywords: COVID-19; disease transmission; independent action hypothesis; respiratory disease; speech droplet.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Air Microbiology*
  • Betacoronavirus / physiology*
  • COVID-19
  • Coronavirus Infections / transmission*
  • Dynamic Light Scattering
  • Fomites / virology
  • Humans
  • Pandemics
  • Particle Size
  • Pneumonia, Viral / transmission*
  • SARS-CoV-2
  • Saliva / chemistry
  • Saliva / virology*
  • Severe acute respiratory syndrome-related coronavirus
  • Speech
  • Viral Load