Here are a few important clarifications on the use of masks in regards to Covid-19.
1. The standard medical/surgical masks or cloth masks do not offer protection for the individual wearing them. These masks are utilized as a "herd protection" measure to prevent the spread of infectious agents from the individual wearing them. This type of masks can only minimize aerosolization and the spread of infectious fluid from the wearers. This type of mask does not have filters to prevent the breathing in of Covid-19.
2. To prevent breathing in the Covid-19 virus, one must wear a filtered mask. N95 (and KN95 - a Chinese specification and approved by the FDA) is the typical mask which has a filter capability to filter out at least 95% of 0.3 um particles. N100 or P100 masks offer additional protection, with almost 99.99% filtering but are less used due to their bulky size.
3. In order for medical/surgical masks to work as in "herd protection," everyone should wear the mask. For those who do not wear the mask, you are a potential source of infection to others nearby (via respiratory and distance via contact contamination)!
Remember to wear a mask and take appropriate safety precautions as we continue combating Covid-19.