Do you breathe out only carbon dioxide?

No! You breathe in and breathe out air containing Oxygen (O2), Nitrogen (N2), Carbon dioxide (CO2), water vapours and other gases present in air. But there is a difference in percentage of O2 and CO2 in exhaled and inhaled air. While percentages of N2 and noble gases are same. read more

You breathe out 16% oxygen, 4% carbon dioxide, some water vapour and the other gases which your lungs mostly ignore. A little carbon dioxide in the blood actually helps maintain the blood pH balance. If you start breathing very quickly, you may get dizzy and lightheaded. read more

Well, okay. Yes, you do breathe in oxygen and breathe out carbon dioxide, which is why you're still alive. Fine. But you also breathe in plenty of carbon dioxide and breathe out plenty of oxygen. It's a lot more complicated than the diagram you remember from third grade where the people are pumping out carbon dioxide and the trees are pumping out oxygen. read more

The carbon dioxide content in our blood is actually what drives breathing, instead of our body’s need for oxygen! Our blood likes to stay in a very narrow pH range (7.35–7.45), and carbon dioxide brings this pH range lower via the enzyme carbonic anhydrase. read more

Its the composition of the atmosphere that makes it such that we breath in oxygen and breathe out carbon dioxide. The concentration of carbon dioxide that builds up in our blood is high compared to the atmosphere which contains almost no carbon dioxide, so essential carbon dioxide is exhaled through diffusion. read more