Masks have a certain shelf life. Generally, the shelf life of masks is 2-3 years, and some can reach 5 years. Generally, masks should not be used beyond the shelf life as far as possible. If masks expire, it is recommended not to use them, which may cause skin allergy, eczema and other allergic phenomena. Gauze masks novel coronavirus can be used by cleaning, but gauze masks can not prevent droplet transmission, nor can they prevent new coronavirus infection. Gauze masks can only protect against steam or larger particles. It is recommended not to use disposable masks. Originally, the medical masks require sterilization. If the medical masks expire, the sterilization effect cannot be guaranteed. The masks are fully sterilized before leaving the factory, so it may not be guaranteed whether sterilization or other problems are still needed after the expiration of the warranty period. But some reports say that the aperture of the expired mask is the same as before, which can prevent virus, but it is recommended to replace it in time.