How Much Carbon Monoxide Is in a Cigarette?

A single conventional cigarette produces roughly 5 to 20 milligrams of carbon monoxide in its mainstream smoke, depending on the brand, filter design, and how it is smoked. That range comes from machine-smoking tests of dozens of brands, with the gas making up about 1 to 5 percent of the smoke by volume. But those machine numbers only tell part of the story, because the way you hold, puff, and inhale a cigarette dramatically shifts how much CO actually enters your bloodstream.

Where the Carbon Monoxide Comes From

Carbon monoxide forms inside a cigarette through two overlapping processes. The first is straightforward combustion: oxygen in the air reacts with the carbonized tobacco at the burning tip, generating CO along with carbon dioxide, hydrogen, and the heat that keeps the cigarette lit.1Progress in Energy and Combustion Science. Smoke generation inside a burning cigarette: Modifying combustion to develop cigarettes that may be less hazardous to health The second is thermal decomposition, sometimes called pyrolysis, where heat breaks down organic materials in the tobacco without enough oxygen for full combustion. Sugars, cellulose, and other carbohydrates in the leaf all decompose this way, adding to the CO output.2Journal of Analytical and Applied Pyrolysis. The pyrolysis of tobacco ingredients Both pathways run simultaneously, and together they account for why CO is one of the most abundant gases in cigarette smoke.3Progress in Energy and Combustion Science. Product formation mechanisms inside a burning cigarette

The 5 to 20 Milligram Range and Why It Varies

A classic study measuring CO yields across a range of conventional cigarettes found that individual brands produced anywhere from 5.0 to 20.2 mg of carbon monoxide per cigarette, which translates to roughly 1.3 to 4.7 percent of the smoke by volume.4PubMed Central. Carbon monoxide yields of cigarettes and their relation to nicotine yield and type of filter That fourfold difference between the lowest and highest brand is not random. Several design features push the number up or down.

The biggest single factor is filter ventilation. Many cigarettes have tiny holes laser-drilled into the filter paper that dilute the smoke with ambient air, lowering the CO reading on a smoking machine. The problem is that real smokers routinely cover those holes with their lips or fingers, undoing the dilution. In one study, blocking the vents on very low-yield cigarettes (1 mg tar by the FTC method) boosted CO exposure by 85 percent for one brand and a staggering 239 percent for another.5PubMed. Effect of filter vent blocking on carbon monoxide exposure from selected lower tar cigarette brands Higher-yield brands with less ventilation showed smaller or negligible increases when blocked, because there was less ventilation to negate in the first place. When vents on all brands tested were fully blocked, every cigarette produced essentially the same CO exposure regardless of what the label claimed.5PubMed. Effect of filter vent blocking on carbon monoxide exposure from selected lower tar cigarette brands

Follow-up research confirmed this wasn’t just a lab artifact. Smokers who habitually blocked their vents on their first cigarette of the day showed about 30 percent greater CO boost from a blocked cigarette compared to an unblocked one, and their total puff volume predicted how much CO they absorbed.6PubMed Central. Filter Vent Blocking on the First Cigarette of the Day Predicts Which Smokers of Light Cigarettes Will Increase Smoke Exposure From Blocked Vents The same pattern held for the best-selling “light” brand in the United States at the time: blocking the vents produced a significant jump in CO.7PubMed. The effect of filter vent blocking and smoking topography on carbon monoxide levels in smokers

All of this means the number on a package or a regulatory database is the yield under standardized machine conditions, not what a person actually inhales. You can think of the 5-to-20 mg range as the floor, with real-world intake often landing higher depending on smoking habits.

How Machine Testing Works and Why It Misleads

The first standardized method for testing cigarette smoke was created by the U.S. Federal Trade Commission in 1966. Over the following decades, CORESTA (an international tobacco research body) and then the International Organisation for Standardisation (ISO) refined the protocol, harmonizing puff volume, puff duration, and the length of the butt left unsmoked. By 1991 an ISO standard was in wide use, and its stated purpose was to compare yields between cigarettes smoked under identical conditions, not to estimate what any individual smoker would inhale.8Beiträge zur Tabakforschung International/Contributions to Tobacco Research. The Development and Significance of Standards for Smoking-Machine Methodology

Canada later introduced its own more intensive machine regime (sometimes called “Canadian Intense”) that uses larger puff volumes and blocks filter vents during testing, producing substantially higher emission readings for the same cigarette. The gap between ISO and Canadian Intense results across hundreds of Canadian brands illustrates how sensitive CO yield is to puffing conditions.9PubMed Central. Revising the machine smoking regime for cigarette emissions: implications for tobacco control policy Neither number perfectly captures real smoking, but the more intense protocol comes closer to what heavier smokers actually do.

How Much CO Your Body Actually Absorbs

Not all the CO in a puff makes it into your bloodstream. Studies of smoke retention in the human respiratory tract estimate that about 55 to 65 percent of inhaled carbon monoxide is retained per puff, with the rest exhaled back out.10PubMed. The retention of tobacco smoke constituents in the human respiratory tract That retention rate is lower than for nicotine or aldehydes (both above 90 percent), because CO is a small, relatively inert gas that doesn’t stick to moist surfaces the way particles and heavier vapors do. Still, 55 to 65 percent of every puff across an entire cigarette adds up quickly.

Once absorbed, CO binds to hemoglobin in your red blood cells, forming carboxyhemoglobin (COHb). In a study of 85 outdoor smokers, the average COHb level was about 2.7 percent at baseline and peaked at 3.1 percent after smoking, compared to roughly 1.3 percent in non-smoking controls.11PubMed Central. Carboxyhemoglobin Levels Induced by Cigarette Smoking Outdoors in Smokers Those numbers may sound small, but COHb levels above 2 to 3 percent start to reduce the oxygen-carrying capacity of blood in measurable ways, and pack-a-day smokers can sustain levels well above that throughout the day.

Exhaled CO as a Smoking Marker

Clinicians and researchers often measure exhaled carbon monoxide (eCO) with a handheld device because it gives a fast, non-invasive snapshot of recent smoking. One study found that a cutoff of 6.5 parts per million correctly identified smokers with 90 percent sensitivity and non-smokers with 83 percent specificity.12Respiratory Medicine. The measurement of exhaled carbon monoxide in healthy smokers and non-smokers Another study in a larger group of over 600 people arrived at a slightly lower cutoff of about 3 ppm for distinguishing smokers, though that threshold had lower sensitivity and very high specificity.13PubMed Central. Assessment of Carbon Monoxide in Exhaled Breath using the Smokerlyzer Handheld Machine: A Cross-Sectional Study The discrepancy reflects differences in study populations, how recently participants had smoked, and how heavily they smoked. As a rough guide, a non-smoker’s exhaled CO is usually around 1 to 3 ppm, while a regular cigarette smoker typically blows somewhere between 10 and 30 ppm shortly after smoking.

Exhaled CO tests are widely used in smoking-cessation programs to give participants immediate feedback and in research to verify self-reported abstinence. The measurement is simple and cheap, though it has limits: CO is not unique to tobacco smoke, so readings can be elevated by gas stoves, heavy traffic, or occupational exposures.14Tobacco Control. Environmental monitoring of secondhand smoke exposure

How Other Smoked Products Compare

Cigarettes are far from the only source of inhaled CO, and some alternatives produce more of it per session than a person might expect.

The takeaway from these comparisons is that combustion is the key variable. Products that burn plant material or charcoal produce the most CO. Heated tobacco products, which avoid combustion, produce very little. E-cigarettes fall somewhere in between in measured exhaled CO, likely because their liquid contains trace organic compounds that can generate small amounts of CO when vaporized at high temperatures, though far less than a flame would produce.

CO in Secondhand Smoke

Carbon monoxide from cigarettes doesn’t only affect the person holding them. In an era before indoor smoking bans became widespread, monitoring in Polish pubs found average 8-hour CO concentrations of about 1 ppm, with some venues spiking above 10 ppm at points during the evening. About 9 percent of the pubs tested exceeded the World Health Organization or European Union limit at some point during monitoring.21PubMed Central. Exposure to carbon monoxide from second-hand tobacco smoke in Polish pubs Those numbers are modest compared to what the smoker inhales directly, but they accumulate during long shifts for bar staff and in homes where someone smokes indoors.

CO has historically served as a marker for secondhand smoke in environmental monitoring studies because it is easy to measure with portable sensors, even though it is not unique to tobacco. Researchers note that CO measurements are especially useful for detecting cigar smoking in indoor environments, where the high CO yield of cigars produces a clearer signal.14Tobacco Control. Environmental monitoring of secondhand smoke exposure For hookah lounges, the problem is amplified by the charcoal factor: a single waterpipe session dumps roughly 30 times the sidestream CO of one cigarette into the surrounding air.16Atmospheric Environment. Comparison of carcinogen, carbon monoxide, and ultrafine particle emissions from narghile waterpipe and cigarette smoking

What Cigarette-Derived CO Does to Your Body

People tend to lump carbon monoxide in with “all the bad chemicals in cigarettes,” but CO has its own distinct set of effects that are worth understanding separately. Its primary harm is competitive: CO binds to hemoglobin about 200 times more avidly than oxygen does, so even modest amounts reduce the blood’s oxygen-carrying capacity. For smokers maintaining COHb levels of 3 to 8 percent throughout the day, tissues chronically receive slightly less oxygen than they should.

In pregnancy, that oxygen deficit matters enormously. Experimental evidence showed that cigarette smoking caused a consistent drop in fetal oxygen levels, and the timing of the decline pointed to carboxyhemoglobin as the most likely cause rather than nicotine or other smoke components. The same oxygen drop occurred even with nicotine-free cigarettes.22PubMed. Maternal smoking causes fetal hypoxia: experimental evidence This fetal oxygen deficit is thought to contribute to the cognitive and behavioral changes sometimes observed in children exposed to tobacco smoke before birth, alongside nicotine’s own effects on the developing brain.23Biomedicine & Pharmacotherapy. Cigarette smoke and related risk factors in neurological disorders: An update

In the brain, prolonged CO exposure triggers oxidant stress in blood vessel walls and can selectively damage specific regions, including central white matter and certain deep-brain structures, through mechanisms related to oxygen deprivation and subsequent inflammatory damage when blood flow returns.24PubMed. Cerebrovascular effects of carbon monoxide These effects are more relevant to acute CO poisoning than to everyday smoking levels, but they illustrate why chronic low-grade CO exposure is not trivial for the vascular system.

Interestingly, a controlled study that delivered CO alone at concentrations matching what cigarette smokers typically get found no significant short-term effect on blood pressure, heart rate, platelet clumping, or inflammation markers. The cardiovascular stress that smokers feel after lighting up appears to come mostly from nicotine and other smoke components, not from CO itself.25Journal of the American College of Cardiology. Cardiovascular effects of carbon monoxide and cigarette smoking CO’s harm is more insidious: it quietly reduces oxygen delivery rather than spiking heart rate or constricting arteries. That chronic oxygen theft, rather than dramatic acute events, is what makes it relevant to smoking-related disease over the long term.

When Smoking Meets Polluted Air

For smokers who live or work in areas with heavy air pollution, CO exposure from cigarettes is not an isolated problem. A study in Beijing found that long-term exposure to high levels of particulate matter and sulfur dioxide reduced lung function in both smokers and non-smokers, but the effect was significantly worse in smokers than in never-smokers.26PubMed. Synergistic effects of air pollution and personal smoking on adult pulmonary function The interaction was synergistic, meaning the combined damage exceeded what you would expect from simply adding the two exposures together. While this study looked at overall lung function rather than CO specifically, the implication is clear: a smoker living in a polluted city is loading additional CO from ambient sources on top of what each cigarette delivers, and the biological effects compound in ways that neither source alone would predict.

This is worth keeping in mind for anyone who smokes in an urban environment or in occupations with combustion exposures, such as cooking over gas, welding, or working near diesel engines. CO from cigarettes does not exist in a vacuum. It stacks on top of whatever background CO your lungs are already handling, and your hemoglobin does not distinguish between CO molecules from different sources.