Carbon monoxide is toxic to humans and animals that uses haemoglobin to transport oxygen.
Simply put – haemoglobin is a protein found in red blood cells that binds oxygen and allows the cells to transport oxygen around our body. (the “Haem” bit gives red blood cells, and indeed blood, its lovely red colour).
However – like much of biology – things “bind” together because they have an affinity or attraction to each other. The higher the affinity, the more likely they are to bind. This is not a specific process though – because other things can bind to haemoglobin.
Specifically, carbon monoxide can bind to haemoglobin, and it has a much higher affinity for haemoglobin than oxygen. In other words – the carbon monoxide binds to the red blood cells at the expense of oxygen.
This means oxygen cannot bind to the red blood cells, so it cannot be transported around your body, so your body is deprived of oxygen and this is, clearly, a toxic situation!
Carbon monoxide is especially dangerous as it has no smell, no colour and no taste. So every house that uses gas should have a carbon monoxide detector that goes off a bit like a smoke alarm.
That way, if you are exposed, you can get treated in the hospital.