Why do we not breathe back in the CO2 we just breathed out?


We don’t breathe out with much force, and even if we did, we immediately inhale. So, how do we not just inhale what we just exhaled?

In: 14

It mixes with the rest of the air so it’s not 100% what we breathed out, but there’s a decent component of it.

Regardless, though — we actually exhale _most of the oxygen we inhale_. You don’t consume all the oxygen you breathe in. Air you inhale is about 20% oxygen, and air you exhale is about 14% oxygen.

This is why you can give people mouth-to-mouth resuscitation, BTW (and yes I know that’s no longer recommended).

We do “reuse” a bit of air with each breath, but we don’t use up 100% of the oxygen with each breathe and we don’t breathe out 100% CO2 either. You can actually 100% rebreathe the same breathe several times and be perfectly ok, they use this concept for some SCUBA technologies to extend how much air you carry.

In case it’s your next question, it’s actually better for us to “keep” a bit of air with each breathe because our lungs don’t “re-open” very well, they work best when they’re already open a little bit. If you lung got 100% empty, you’re probably not be able to reopen them and you’d suffocate to death.

You do get some recycling in a stale room, but the air you exhale hasn’t been fully depleted of oxygen either.

Fresh air is 21% oxygen, and the air you exhale is 17%.

Gases do disperse very quickly (watch a smoker sometime) so you’re not just recycling the same quarter-lungful when you’re sitting down. Outside even a slight breeze will fully exchange the air in a second.

You do. Some of it at least. You are exhaling way less CO2 than you likely think.

When you inhale, you’re taking in 78% nitrogen, 21% oxygen, 0.04% CO2.

You exhale 78% nitrogen, 17% oxygen, 4% CO2, and the rest various gasses.

Just look at someone who vapes and just breathes out normally. The aerosol does disperses quite a lot and it is pretty obvious why you do not just breath in the same air.

The white stuff you see when someone vape is not vapor, it is an aerosol. Vapor is a gas and is invisible to us. What you see are small liquid droplets just like a cloud or fog, clouds can contain solid ice too. Droplets or solid suspended in air is called an aerosol