Studies have found that the virus remains on surfaces for up to 9 days, and after that, it is permissible to re-use the mask. Of course, this is not the ideal situation nor recommended. In ideal circumstances with an adequate supply of disposable masks, they would be single use products. However, in light of the shortages that are occurring, it is advised that you have several masks on rotation, so that you can ensure that each time you use a certain mask, it will not be contaminated.
If you want to prolong the life of your disposable face mask, make sure you always remove it using the ear straps, and not touching the surface of the mask. You can then place your mask in a “clean receptacle” like a paper bag or something else similar that allows the mask to safely air out. You should not use any sort of disinfectant spray because it will absorb into the material and then you’ll end up breathing it in. It is best to let your mask sit for a few days in a clean receptacle before wearing it again.
Of course, if your mask becomes visibly dirty or torn, you should just throw it out.
For healthcare professionals, respirators can be used beyond the manufacturer designated shelf life. In a crisis situation, it is also permissible to use a disposable mask for a patient, then remove it and store it for use with another patient (this can be done multiple times before disposing of the mask).