If the mask expires, it is recommended not to use it. The mask is generally valid for 3-5 years, some may be short and some may be long, and the mask may cause skin allergy and eczema after it expires. If it is a gauze mask can be used by washing, but gauze masks cannot prevent new coronavirus infection. Disposable masks such as medical surgical masks or N95 masks should not be used after the expiration date. Medical masks require disinfection and sterilization, and if they exceed the shelf life, this may not be guaranteed. If they can be fully sterilized, they can continue to be used, but the protective ability of such masks will be reduced, so it is recommended to replace them with new factory masks in a timely manner. Content source: Dr. You Lai