At present, there is no clear conclusion on the optimal wearing time of N95 masks abroad, including WHO, and China has not yet made relevant regulations on the use time of masks. Some researchers have conducted relevant research on the protection efficiency and wearing time of N95 medical protective masks. The results show that the filtration efficiency of N95 masks is still above 95% for 2 days, and the respiratory resistance does not change much; the filtration efficiency is reduced to 94.7 after 3 days %. The recommendation given by the US CDC is that in the absence of an adequate supply of masks, as long as the device is not significantly soiled or damaged (such as creases or tears), it can be considered for reuse.

When the following conditions occur, the mask should be replaced in time:

1. When the respiratory impedance increases significantly;

2. When the mask is damaged or damaged;

3. When the mask and face cannot be in close contact;

4. The mask is contaminated (such as blood stains or droplets).

5. Used in individual wards or patient contact (because the mask has been contaminated)