English: Plot of the probability density function for droplet size, for droplets breathed out by someone speaking, using fit to experimental data of Johnson and coworkers (Journal of Aerosol Science, 42, p 839 (2011)https://doi.org/10.1016/j.jaerosci.2011.07.009). Larger values along the y axis mean more droplets, and the x axis is the size of the droplet. Our breath contains tiny droplets of mostly mucus, produced in our lungs, throat and mouth. The vast majority of these droplets are too small to be seen but are responsible for the transmission of diseases such as COVID-19 and tuberculosis - the droplets can contain viruses and bacteria. The droplets range in size from much less one than one micrometre up to around a millimetre. The small droplets around one micrometre are much more numerous than larger droplets.