Under normal circumstances, an N95 mask can not be worn for more than 4 hours, and can be reused when the supply of N95 masks is insufficient. The principles of use are as follows: 1. Extended use period: If you do not take it down after wearing, you can extend the use time appropriately; 2. Limited reuse: Subject to the manufacturer’s regulations, it can be reused, but generally not more than 5 times. As the filtration efficiency of N95 mask will gradually decrease with the use of time, in order to make better use of the mask, you need to wash your hands according to the protocol, avoid touching the inside of the mask when wearing it, and replace it immediately when the mask is contaminated, appears wet, broken, etc.