UCSB Science Line
Carbon monoxide (CO) is very dangerous because it sticks to your hemoglobin better than oxygen does. It "hogs the seats" so that oxygen can't get a ride. And those CO molecules keep riding around, never giving their seats up to the oxygen. This means there's no way to get oxygen to your brain, heart, or other cells and those cells start to die. The chemical reactions that stop happening when there's no oxygen are the ones that make ATP, the form of energy that all of our cells use.