It depends. If there is no unsealed mask, and the mask is still within the shelf life, it can still be used. Otherwise, it is recommended not to take risks. If it is an unopened mask, it is recommended not to use it, whether it is expired or not. The shelf life varies from product to product. You can refer to the product description. How long is the shelf life if it is opened? Don't use it after the expiration date!
The mask must not be placed vertically, so that the essence of the mask will flow to the bottom. The next time you open it, you'll find it all dry or the essence is gone. If you are a smear mask, you can still use it by comparing the patterns on the back of your mask, which will not exceed the shelf life, but it contains many active ingredients, so you should use it early and frequently in the future to make your skin feel the good of this mask.
If there is an inner package and it is kept fresh in the refrigerator, it should be available if it has not passed the shelf life. It's basically useless without saving it. Throw it away. Otherwise, it will damage your beautiful face. If it is a one-piece mask, it can't be used after half a year; If it is a smear mask, it can still be used as long as it is within the shelf life.
If you are in a disposable bottle, the active ingredients in it have evaporated and can't be used. It is recommended to use patch mask. The best time to apply the mask is 15-20 minutes. Many people think it's only 20 minutes, but the mask is still wet.