How does carbon monoxide in cigarette smoke affect the blood’s ability to carry oxygen?

Carbon monoxide in cigarette smoke significantly impairs the blood’s ability to transport oxygen throughout the body. This occurs because hemoglobin—the protein in blood responsible for carrying oxygen—has a much higher affinity for carbon monoxide than for oxygen.1

When inhaled, carbon monoxide binds to hemoglobin to form a stable compound known as carboxyhemoglobin. Because this bond is highly stable and difficult for the body to break down, the carbon monoxide effectively occupies the sites on the hemoglobin molecules that would otherwise be used to transport oxygen. Consequently, there are fewer hemoglobin molecules available to carry oxygen to the body's tissues.123

This reduction in oxygen-carrying capacity forces the heart to work harder to maintain adequate oxygen delivery, which increases the risk of cardiovascular disease, myocardial infarction, and stroke.3