KN95 masks cannot be used repeatedly, and generally need to be replaced in about 4 hours, depending on the environment in which they are used. KN95 masks are masks produced in our country with international N95 standards, and can filter more than 95% of non-oil particles. Even in a normal outdoor environment or a closed indoor environment without viruses and microorganisms, this mask cannot be used repeatedly. Because the filtering function is decreasing with time, especially in high-risk places such as hospitals, wards and fever clinics, and in crowded places such as hotels, public places and theaters, the mask needs to be replaced once every 4 hours. If there is a spattering or pollution, it is necessary to change the mask at any time.