Carbon monoxide (CO) is a significant and poisonous component found in cigarette smoke. This toxic gas is colorless, odorless, and tasteless, making it impossible to detect without specialized equipment. Once inhaled, CO enters the bloodstream and directly interferes with the body’s ability to transport oxygen throughout the tissues and organs.
Where Carbon Monoxide Comes From
Carbon monoxide is not an intentional ingredient added to tobacco, but an unavoidable byproduct of combustion. It is produced when carbon-containing material, such as the tobacco leaf, paper, and additives, burns without a sufficient supply of oxygen. This chemical process is known as incomplete combustion.
During smoking, the tobacco smolders. The limited oxygen supply in the burning cone prevents the carbon from being completely converted into carbon dioxide (CO2). Instead, this incomplete reaction yields a high concentration of carbon monoxide (CO), which is mixed into the smoke inhaled by the user.
How Carbon Monoxide Starves the Body of Oxygen
The toxicity of carbon monoxide stems from its powerful attraction to hemoglobin, the protein inside red blood cells responsible for carrying oxygen. When CO is inhaled, it rapidly passes into the bloodstream and binds to the heme sites on the hemoglobin molecules.
This binding process creates a stable compound called carboxyhemoglobin (COHb). Carbon monoxide has an affinity for hemoglobin that is approximately 200 to 300 times greater than that of oxygen. This means CO effectively outcompetes oxygen for the binding sites, even when present in low concentrations.
As COHb levels build up in the blood, the total oxygen-carrying capacity of the red blood cells drops significantly. Hemoglobin molecules bound to CO are no longer available to transport oxygen from the lungs to the body’s tissues. Furthermore, COHb causes the remaining oxygen-carrying hemoglobin to hold onto its oxygen more tightly, making it harder to release oxygen to the organs that need it. This dual mechanism results in the starvation of the body’s cells for oxygen.
Immediate and Chronic Health Effects
The immediate effects of carbon monoxide exposure are tied directly to the formation of carboxyhemoglobin (COHb). Chronic smokers often maintain COHb levels between 3% and 8%, while heavy smokers can reach 15%. Even at concentrations as low as 5%, healthy individuals may experience a reduced capacity for physical exertion because their muscles and heart receive less oxygen.
For people with pre-existing heart conditions, symptoms can worsen at COHb levels as low as 2%. Symptoms of mild CO poisoning, such as headache, dizziness, or nausea, can occur at higher concentrations, mimicking the flu. Chronic exposure significantly burdens the cardiovascular system.
The heart must pump harder and faster to compensate for reduced oxygen delivery, increasing its workload. This sustained stress contributes to serious issues, including atherosclerosis, the buildup of plaque in the arteries. Carbon monoxide exposure is directly linked to an increased risk of heart attacks and strokes because it promotes oxygen debt and damage to the circulatory system.
Exposure Levels in Different Tobacco Products
Carbon monoxide exposure varies significantly across different tobacco and nicotine delivery products. Traditional combustible cigarettes are a consistent source, but other forms of tobacco can result in even higher concentrations.
Cigar and water pipe (hookah) smoking involve larger volumes of smoke and longer duration of use, leading to extremely high CO exposure. Water pipe use has been reported to cause COHb levels as high as 39.2%, a level associated with acute toxicity. Secondhand smoke is also a recognized source of carbon monoxide, exposing non-smokers in the vicinity.
In contrast, modern non-combustible products show a substantial difference in CO output. Heated tobacco products (HTPs) operate by heating tobacco rather than burning it, which significantly reduces CO production. Studies measuring exhaled CO levels in users of HTPs and electronic cigarettes typically show no elevation or levels significantly lower than those from traditional cigarettes.