How is it not dangerous to breathe in the CO2 that we breathe out into our masks?

Question

I’ve heard a lot of anti-maskers use the argument that since we breathe out CO2, it will become trapped in the mask and is dangerous to breathe back in.

Obviously, this isn’t the case, because doctors wear their masks for hours and hours on end while doing surgeries. However, I am wondering, how does it work?

In: Biology

Answer 1

Your lungs have a volume of around 2 liters. The space inside your mask has a volume of a few millilitres. When you breathe 2 litres of gas out, around 0.01% of that stays in your mask. When you breathe in 2 litres of gas, 99.99% is fresh air and 0.01% is the stale air trapped in your mask.