I have checked my blood oxygen after wearing a mask for 2 minutes. There is a significant drop in O2 levels.
My oxygen sats without a mask and normally are 97% 98% with a mask they are 87% or even 86%, Medicare will pay for a patient to go home on oxygen and set up a tank of oxygen at their home and have it delivered for anyone whose sats are below 88%.
Vital organs do not get enough oxygen below 88% which is why they do this.
Check your O2 levels while wearing a mask with your baseline being testing with no mask.