Which category best describes carbon monoxide?

• A. Neurotoxin
• B. Asphyxiant
• C. Carcinogen
• D. Poison

Answer: (B)

Carbon monoxide is best described as an asphyxiant because its primary harm comes from depriving tissues of oxygen. It binds to hemoglobin with a much higher affinity than oxygen, forming carboxyhemoglobin, which drastically reduces the blood’s capacity to carry O2 and makes it harder for tissues to receive the oxygen they need. This oxygen deficiency leads to hypoxia and suffocation-like effects, which is the defining feature of an asphyxiant. It isn’t a carcinogen, since it doesn’t cause cancer, and while neurological symptoms can occur, they’re a consequence of hypoxia, not direct neurotoxicity. So the mechanism driving the harm is best captured by labeling it an asphyxiant.