I’m sure that wearing a mask has its own health hazards because it cuts the flow of oxygen, forces the wearer to breathe in the CO2 he exhaled, and quickly gets contaminated with the microbes that he exhaled.
Not just that, they concentrate virus and other particulate that your body is trying to get rid of in your nasal cavities and make it more likely that you will get sick. Below a certain threshold your bodies other defenses can fight off most pathogens, above that you get sick... if you have a compromised immune system this threshold is lower.