Not only can re-usable masks be cleaned and washed, but it is also encouraged that you do so after each wear.
If you feel that you might have been exposed to a virus – if somebody sneezes on you while you are standing in line somewhere, for example – you should take extra care.
In such cases, it’s best to rather dispose of your mask in a plastic bag and wash your hands thoroughly after doing so.
You should do this as soon as you arrive at your chosen destination. If you do not want to dispose of your mask, it should remain in the plastic bag for at least three days before being washed on the highest setting the manufacturer’s instructions allow.
Not enough research has been done to definitively say how long the virus lives on fabric surface, which is why it is so important to take care when washing your mask if you believe you have come in contact with the virus.