N90 masks protect against droplets with viruses, but not against viruses. Viruses are nanoscale, and N series masks can be used to protect against non-oil suspended particles, but not against nano-scale viruses themselves. Generally speaking, masks are worn to block non-oil suspended particles such as droplets of saliva and body fluids with coronaviruses. In comparison, 3M’s N90 mask is better than disposable surgical masks in terms of protection because the 3M mask fits perfectly on the face and there are no air leaks. The medical disposable surgical mask filtration efficiency is only 70%, and not sealed around, but can be used as ordinary protection.