Wearing masks is common in several asian countries even before c19 was a thing and I'm not aware of anyone showing that it's causing harm at the population leve

Wearing masks is common in several asian countries even before c19 was a thing and I'm not aware of anyone showing that it's causing harm at the population level. I consider that reasonable evidence that wearing them has no significant negative physiological effects. I could see negative behavioral effects such as making people more careless because they're feeling safer. But again, effective containment in above-mentioned countries would also serve as evidence against that actually being an issue.