When carbon monoxide is inhaled, it is readily absorbed through the lungs and into the bloodstream where it binds to the Fe center in hemoglobin (see also “Biochemistry”). Unfortunately, hemoglobin binds to carbon monoxide much more strongly than it does to oxygen, so carbon monoxide rapidly interferes with the ability of hemoglobin to deliver oxygen throughout your body. If this happens, then your muscles and your brain will begin to run out of oxygen, similar to what happens when a person is drowning! Carbon monoxide is a colorless, odorless gas, which makes it difficult to detect unless you have a carbon monoxide detector around. Carbon monoxide levels of 100 parts per million or higher can be hazardous or fatal to humans.

Poisoning from carbon monoxide can result in brain damage, damage to the endocrine system, to the nervous system, and to the heart and other organs. It represents the leading cause of accidental poisoning-related death and poisoning-related injury globally. We should mention that even if a person survives carbon monoxide poisoning, there may be long-lasting effects. Early symptoms of carbon monoxide poisoning can include headaches or nausea, and the treatment for carbon monoxide poisoning typically involves having a person breathe 100% O₂ (recall that air only contains ca. 20% O₂), so that O₂ can more competitively bind hemoglobin to replace carbon monoxide.