Disposable medical masks are generally not recommended to be used twice and should be replaced if worn continuously for no more than four hours. If resources are very tight or if the time spent wearing it once is really short, you can also wear it twice. The method is to fold the inside of the removed mask inward and then fold it again and place it in a dry, ventilated place where it can be applied again for a short time. However, it is not recommended to use it again if the following conditions occur: 1, the mask is broken; 2, the inner and outer surface of the mask is contaminated by visible pollutants; 3, the mask is soaked with water, sweat, saliva and other liquids. The recently mentioned on the network will wear the mask with alcohol disinfection or heating disinfection are not scientific, one is not complete disinfection, the other also destroyed the function of the mask, lose the original role of the mask.