Every time you inhale cigarette smoke, more than 7,000 chemicals and compounds—including cadmium (a component of battery acid), acetone (found in nail polish remover) and arsenic (used in rat poison)—flood into your body. Within seconds of your first puff, these harmful gases (plus others, like formaldehyde, ammonia and hydrogen sulfide) begin to irritate the sensitive membranes of your eyes, nose and throat.
As the smoke passes into your lungs, carbon monoxide (the same gas found in automobile exhaust) is immediately transferred to your blood, where it binds to oxygen receptor sites and kicks oxygen molecules out of your red blood cells. This means less oxygen makes its way to your brain and other vital organs.
After eight hours smoke-free, the carbon dioxide and oxygen levels in your blood return to normal, and the damage caused by carbon monoxide (and the other chemicals found in cigarettes) begins to reverse.