To determine whether the mask is regular or not, check the packaging of the mask, whether the packaging of the mask is tight, and at the same time whether there is a regular manufacturer on the packaging of the mask. In addition, whether the packaging of the mask identifies the production date and expiration date, and whether there are instructions for use of the mask on the packaging of the mask. After opening the mask package, check whether the mask is deformed or whether the mask has a bad smell. Usually the middle of a regular mask is the filter layer, which can filter bacteria or viruses invading the human respiratory system and causing disease. The filtering of medical surgical masks can reach about 30%, while the filtering of medical N95 masks can reach more than 95%. After using the mask, it is recommended to place it in a ventilated, cool and dry place to prolong the life of the mask.