Regarding the replacement frequency, currently, there is no clear conclusion on the optimal wearing time of N95 masks in foreign countries, including WHO, and there is no relevant regulation on the use time of masks in China. Some researchers have conducted relevant studies on the protective efficiency and wearing time of N95 medical protective masks. The results show that the filtration efficiency of N95 masks remains above 95% and the respiratory resistance changes little after wearing them for 2 days. Wear for 3 days filter efficiency reduced to 94.7%.

However, masks should be replaced when:

1. When respiratory impedance significantly increases;

2. When the mask is damaged or damaged;

3. When the mask is not in close contact with the face;

4. The mask is contaminated (if there are blood stains or foreign matters such as droplets);

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

6. If the mask contains activated carbon, if there is an odor inside the mask.