Wearing a mask when you are healthy and not actually working with sick patients, grants you:
https://www.google.ca/url?sa=i&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHypercapnia&psig=AOvVaw0DrLh2aXtacFgMKT-7il2t&ust=1588795346347000&source=images&cd=vfe&ved=2ahUKEwi_jpiDwp3pAhUUBzQIHdM9A9EQr4kDegUIARD3AQ