there were numerous studies (showing their effectiveness)

All junk science. Studies on mask effectiveness are based on taking a new mask, gluing it down over an air-input pipe to ensure there is absolutely no air leakage around the edges, and seeing whether or not it blocks virus-sized particles. Well that's just great, except that no actual human being glues the mask to their face. In real life, there is always air leakage around the edges of disposable masks. Even tightly fitted disposable masks don't stay tightly fit all day.

Virus particles are at least 10-100 times smaller than the gaps between the fibres in surgical and N95 masks. To combat that, during manufacture the fibres in N95 masks are charged up with thousands of volts to give them an electric charge of about 10 nanocoulombs, making them into a permanent electret. The electric field attracts microscopic particles to the fibres and traps them. Well, that's the intention, but in practice the electric charge leaks away over time, or when exposed to moist air, or when touched. That's why you're not supposed to re-use masks, or wash them, or even spray them with alcohol. After some hours, the electric charge is completely gone.

That's not a problem for laboratory tests which only last a few minutes, maybe an hour. But the test conditions are nothing like real-world use:

• humans exhale moist air, which causes the electric charge to disperse even faster than it would normally;
• they are often required to wear the masks for many hours at a time, not just a few minutes;
• they frequently need to touch the mask to adjust it, or to take it off to eat or drink;
• if they are wearing it outside they may get caught in rain.

Even if the mask was perfectly effective at blocking viruses at the start of the day, it won't stay that way.

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