What's in a Cigarette: 7,000 Chemicals and 69 Carcinogens

Quick answer: The National Cancer Institute says tobacco smoke contains more than 7,000 chemicals, at least 250 known to be harmful and at least 69 that can cause cancer — the CDC puts the cancer-causing count at "at least 70". They include benzene, formaldehyde, arsenic, cadmium, polonium-210, polycyclic aromatic hydrocarbons and tobacco-specific nitrosamines. Carbon monoxide, hydrogen cyanide and ammonia are harmful but are not on the cancer list. Nicotine drives the addiction.

People know cigarettes are "bad," but the chemistry is often vague. Knowing that you're inhaling the chemical used in embalming, or one found in petrol fumes, can change how the habit feels.

How Cigarette Smoke Is Created

When tobacco burns, it undergoes combustion and heating that break its material down and form new compounds. The smoke has two parts:

Gas phase: carbon monoxide, nitrogen oxides, hydrogen cyanide, volatile organic compounds, ammonia

Particle phase (tar): nicotine, polycyclic aromatic hydrocarbons (PAHs), tobacco-specific nitrosamines, phenols, heavy metals

The National Cancer Institute puts the total at more than 7,000 chemicals, at least 250 of them known to be harmful.

The Carcinogens

The NCI counts at least 69 chemicals in tobacco smoke that can cause cancer, and the CDC says at least 70 are known to cause cancer in people or animals. The NCI's own list names: acetaldehyde, aromatic amines, arsenic, benzene, beryllium, 1,3-butadiene, cadmium, chromium, cumene, ethylene oxide, formaldehyde, nickel, polonium-210, polycyclic aromatic hydrocarbons, tobacco-specific nitrosamines and vinyl chloride. Some of the main ones:

Tobacco-specific nitrosamines (TSNAs)

NNK and NNN
Formed from nicotine and related compounds during curing and burning
Strong carcinogens in animal studies; the tobacco-specific marker NNAL comes from NNK
Found only in tobacco products

Polycyclic aromatic hydrocarbons (PAHs)

Benzo[a]pyrene is the best studied
Formed whenever organic material burns incompletely — also found in charred food and exhaust fumes
Form DNA adducts that can lead to mutations, one of the main routes to smoking-related cancer

Benzene

The International Agency for Research on Cancer (IARC) classifies it as a Group 1 human carcinogen; it causes leukaemia
Also found in petrol vapour and vehicle exhaust

Formaldehyde

IARC Group 1 carcinogen
The same chemical used in embalming and industrial resins

1,3-Butadiene

IARC Group 1 carcinogen
Also found in vehicle exhaust and rubber manufacturing

Metals

Arsenic, cadmium and chromium (VI) are IARC Group 1 carcinogens; beryllium and nickel are also on the NCI list

Polonium-210

A radioactive element on the NCI's list of carcinogens in smoke

We don't print per-cigarette amounts for these chemicals: yields vary widely by brand and by how a cigarette is smoked, and a smoking machine cannot predict what a person actually inhales.

Harmful but Not on the Cancer List

Carbon monoxide

Binds haemoglobin about 245 times more strongly than oxygen, according to the UK Health Security Agency
Around 5–10% of a smoker's haemoglobin carries CO, against 1–2% in non-smokers
Detailed mechanism: Carbon Monoxide and Smoking

Hydrogen cyanide

A poison that blocks cells from using oxygen
On the NCI's list of harmful chemicals in smoke

Ammonia

An irritant, and on the NCI's list of harmful chemicals

Acrolein

A highly reactive, irritant aldehyde
IARC classified it as probably carcinogenic to humans (Group 2A) in 2021

Tar: The Mixture

"Tar" is not a single compound — it's the term for the particulate matter in smoke, minus water and nicotine. It carries PAHs, nitrosamines, phenols and many of the other compounds above. Some of these also cause epigenetic changes that switch genes on or off without altering the DNA code. See What Tar Does to Your Lungs.

Nicotine: The Addictive Agent

Nicotine is not a direct carcinogen. A leading pharmacology review notes concerns that it may promote tumours, based on animal studies, and says whether that happens in people has not been established. Its main role in the harm of smoking is addiction: it binds to nicotinic receptors in the brain and triggers dopamine release, keeping people smoking long enough for the rest of the smoke to do damage. The NHS says nicotine on its own doesn't cause cancer, lung disease, heart disease or stroke — which is why nicotine replacement is used to help people quit.

The Additive Question

Cigarette makers add many compounds — sugars, flavourings, humectants, menthol and others. Some change how the smoke tastes or feels, which can make smoking easier to start and to keep going.

Menthol deserves a mention: it gives a cooling sensation that makes smoke feel less harsh. Menthol cigarettes are not safer.

The Comparative Perspective

WHO says tobacco kills more than 7 million people each year, including over 1.6 million non-smokers exposed to second-hand smoke, and that there is no safe level of exposure.

Sources

National Cancer Institute. "Harms of Cigarette Smoking and Health Benefits of Quitting." cancer.gov
Counts ME et al. "Smoke composition and predicting relationships for international commercial cigarettes smoked with three machine-smoking conditions." Regulatory Toxicology and Pharmacology, 2005. PubMed
Hecht SS. "Cigarette smoking: cancer risks, carcinogens, and mechanisms." Langenbeck's Archives of Surgery, 2006. PubMed
International Agency for Research on Cancer. IARC Monographs, Volume 83: Tobacco Smoke and Involuntary Smoking. 2004.
International Agency for Research on Cancer. IARC Monographs, Volume 128: Acrolein, Crotonaldehyde, and Arecoline. 2021.

Frequently Asked Questions

How many chemicals in cigarettes are carcinogenic?

The National Cancer Institute counts at least 69 chemicals in tobacco smoke that can cause cancer, out of more than 7,000 chemicals and at least 250 known to be harmful. The CDC's figure is at least 70.

Are organic or "natural" cigarettes safer?

No. Burning organic tobacco still produces the same combustion products, and most of the carcinogens in smoke come from burning, not from pesticides or additives.

Does filtering cigarettes remove the toxic chemicals?

Not in practice. The National Cancer Institute explains that people smoking "light" or highly filtered cigarettes take deeper, longer or more frequent puffs, or block the ventilation holes, and can inhale just as much tar as from regular cigarettes.

Are e-cigarettes free of these chemicals?

No, but they contain far fewer of them. E-cigarettes don't burn anything, and the NHS says most of the harmful chemicals in tobacco smoke, including tar and carbon monoxide, are not in vape aerosol. The aerosol still contains nicotine, flavourings and some toxic substances at lower levels, and the NHS says vaping has not been around long enough to know its long-term risks.