There is no good proof they do, there is no good proof they dont. Also, work is subjective, can mean does it work to protect an individual, or does it work to protect others from infected individual.
For their stated purpose no? In fact they are bad for your health via reduced blood-oxygen levels, keeping pathogens and viruses concentrated (a literal germ rag) right next to your air intake (instead of them getting cast away and dispersed), and accelerating tooth decay.
There is no good proof they do, there is no good proof they dont. Also, work is subjective, can mean does it work to protect an individual, or does it work to protect others from infected individual.
There is plenty of good proof that they don’t, because it’s easy to refute every hypothesis that they do.
For their stated purpose no? In fact they are bad for your health via reduced blood-oxygen levels, keeping pathogens and viruses concentrated (a literal germ rag) right next to your air intake (instead of them getting cast away and dispersed), and accelerating tooth decay.
For their intended purposes? Absolutely!