There has been much confusion about the use of masks during the coronavirus outbreak, following initial (and scientifically intemperate) assessments they may not be needed by the general public. We do not know all the details of how the Covid-19 virus transmits via respiratory droplets and through contact with contaminated surfaces, and there isn’t the time to do rigorous experiments. But prior experiments with masks and common scientific sense make it clear that the use of masks, or in their absence, even a scarf wrapped around the nose and mouth, will provide much increased protection as opposed to nothing at all.
Respiratory droplets, sprayed during activities such as coughing or speaking, range in size from about 0.1 microns to a few hundred microns. For comparison, the average human hair has a diameter of about 75 microns. Droplets smaller than 10 microns (also called aerosols) can hang in the air and travel deep into the respiratory passages. Droplets larger than 10 microns tend to get produced during coughing, sneezing or speaking and can travel further. Because of their larger size they can carry larger numbers of viruses. But they can also fall to the ground quicker. They tend to get lodged in the upper parts of the respiratory system.
In 2008, a study by Dutch and American scientists compared the relative effectiveness between a tea cloth, a surgical mask, and a N95 mask against aerosol particles of 0.02-1 micron. As expected, the N95 mask performed the best, blocking at least 99-99.5% of the particles. The surgical mask blocked about 70-80% and the tea cloth blocked about 65% of the particles. The message was clear – a mask or, in its absence, even a scarf around the nose and mouth offers significant protection. Note that the above studies were carried out for particles less than a micron in size – the slippery size at which it is very difficult to trap them.
But it is important to note that scarves and masks that have not been “fitted up” properly will have gaps between its contours and the face. Contamination can come in over time through these gaps. Hence, it is important to continue to avoid proximity to others – stay six feet away and keep the interaction as short as possible. And refrain from adding too many layers to the scarf since it will block airflow to the extent that most of the air will then enter unfiltered through the gaps between the scarf and the skin.