All face masks are not made equal. The extent to which a mask can affect carbon dioxide depends on what it is made of and how tightly you are wearing it.
It’s highly unlikely that you can pass out due to lack of oxygen while wearing a cloth mask, which in most cases doesn’t fit tightly on to your face. When you breathe, the air around the mask travels through pores in the material. It helps by disturbing your exhalation to protect those around you from aerosols in your breath.
Experts doubt that any cloth face mask can ever fit against the face so tight that someone can pass out due to lack of oxygen. In fact, most of us take it off before it becomes too uncomfortable.
An expert says, wearing N95 mask for a prolonged period may have alterations in their blood chemistry that can change the level of consciousness, if severe. This is most likely to happen in those who already have breathing difficulties due to smoking, obesity, COPD or asthma.
Any mask including the N95 has not shown to cause carbon dioxide toxicity in healthy people. Breathing becomes harder with a mask, thus people with existing breathing problems must be careful while wearing a face mask.