Masks pinch the nose, and train people to mouth breathe. Mouth breathing causes all sorts of health issues.
To learn about the negative health impacts of mouth breathing. I highly recommend reading or listening to the book Breath, by James Nestor.
Breath: The New Science of a Lost Art https://www.amazon.com/dp/0241289122/ref=cm_sw_r_apan_glt_i_WDASMVTWJ4SPZTYDHJZA