The short answer
Soot is the black residue from burning fuel. NCI links soot to skin, lung, esophageal, and bladder cancers, and chimney sweeps have the highest exposure. Limiting contact with soot lowers exposure.
Soot is listed as a carcinogen in the U.S. National Toxicology Program's Report on Carcinogens.
People can be exposed by breathing soot, swallowing it, or skin contact, and chimney sweeps have the highest exposure.
NCI links soot to skin, lung, esophageal, and bladder cancers.
A carcinogen classification describes hazard — whether something can cause cancer — not your personal risk at a given exposure.
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The simple version
Soot is the black, powdery material left when wood, coal, or oil burns. The link to cancer was first noticed in 1775, when British chimney sweeps were found to have high rates of scrotal cancer.
What soot is
NCI describes soot as a byproduct of the incomplete burning of materials that contain carbon, such as wood, fuel oil, plastics, and household refuse. Its fine particles may carry harmful substances such as arsenic, cadmium, and chromium. In 1775 British chimney sweeps were noticed to have high rates of scrotal cancer.
How people are exposed
Common ways people come into contact with it:
- Working as a chimney sweep, which NCI says carries the highest exposure.
- Breathing, swallowing, or skin contact with soot from fireplaces, furnaces, and engine exhaust.
The cancer connection
NCI says research links soot to skin cancer (especially scrotal cancer in chimney sweeps), lung cancer, esophageal cancer, and bladder cancer.
The US National Toxicology Program, part of the National Institutes of Health, lists soots in its Report on Carcinogens.
Hazard is not the same as risk
Hazard and risk are easy to run together, but they are separate ideas. Calling soot a carcinogen is a statement about hazard. It says soot can cause cancer under some conditions. It does not describe your personal risk. NCI says chimney sweeps have the highest exposure. A sweep working in chimneys all week is not in the same position as someone who lights an occasional fire. The carcinogen label answers "can it cause cancer?" It does not answer "how likely is that for me?"
How to lower your exposure
- Limit contact with soot, and wash skin after contact.
- If you work with soot, ask your employer about protective equipment and safety practices; NCI says workers should stay informed about changing safety technologies and practices.
Soot is one exposure among many, so it helps to see it in proportion. Our overview of cancer prevention and what raises cancer risk put any single exposure in context.
The bottom line
Soot is a carcinogen listed by the National Toxicology Program. The useful step is knowing when soot lands on your skin or in your lungs, and keeping that to a minimum. A classification is not worth losing sleep over. Give your attention to the risks you can change.
Common questions
Does soot cause cancer?
Soot is listed as a carcinogen by the U.S. National Toxicology Program, and NCI links it to several cancers. How much any one person's risk rises depends on how much they are exposed to and for how long.
How are people exposed to soot?
NCI says people can be exposed by breathing it, swallowing it, or skin contact, for example from fireplaces, furnaces, and engine exhaust. Chimney sweeps have the highest exposure.
Which cancers are linked to soot?
NCI says research links soot to skin (especially scrotal), lung, esophageal, and bladder cancers.
How can I reduce my exposure to soot?
Limiting contact with soot is the main step. Common-sense measures include protective clothing, washing skin after contact, and good ventilation. If you work with soot, ask your employer about safety practices.
Does a carcinogen label mean I will get cancer?
No. A classification is about hazard — whether soot can cause cancer under some conditions — not a prediction that any one exposed person will develop cancer. Your actual risk depends on the amount and length of exposure and other factors.
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Last updated: 2026-10-16Next planned review: 2028-07-05
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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