Masks are actually designed to be worn for only short periods of time in acute situations. They should be changed after interacting closely with any other person for more than 10-15 minutes (obviously this is different for surgeons/surgical nurses/surgical techs who wear sterile masks in a sterile environment while performing lengthy surgeries).
Masks should not be touched while wearing. They should not be stored in a pocket, purse, or stored on the floor or seat of your car. I think a dirty mask presents a myriad of opportunities for infection with numerous things. The risk of transmission of virus by staying 3.3 feet or more away from another person’s face is about 2.6% while it is ~3.1% for perfect mask wearing. If masks were 100% protective, no healthcare workers should have gotten this illness, right?
Bottom line: we can’t hide from this virus (or any other). A strong immune system and good handwashing are very important. Stay out of each other’s faces. Caregivers for the most vulnerable need to be even more cautious than the general public and be sure to use PPE as perfectly as possible.