Even if it does decrease your blood oxygen. I did an experiment with my apple watch. Just sitting, normal breaths, I took several readings alternating mask-on, mask-off with several minutes between readings. With the mask off the mean was 98. With it on, 91. Std deviation was ~.6 with the mask off and 1.2 with it on. I was surprised by the consistency of measuring blood oxygen with a dang watch! I mean, who'd have thought one could measure such things by bouncing red light off your skin?I wear a mask if I am expect to be within six feet of people I do not know. Wearing a mask does not limit my ability to shop, travel or visit with people. I don't agree that wearing a mask infringes on my freedom. Wearing a mask increases my freedom of movement.
It was less consistent with the mask on, which I guess is to be expected. 91 isn't terrible but it's below normal.