The short answer
Arsenic is a natural element that can contaminate drinking water, especially from private wells. Long-term exposure is linked to skin, bladder, and lung cancers. Testing well water and treating or switching sources lowers exposure.
Arsenic is classified as a known human carcinogen (IARC Group 1).
People are mainly exposed by drinking water contaminated with inorganic arsenic, especially from private wells.
It is most strongly linked to bladder, skin, and lung cancers.
A carcinogen classification describes hazard — whether something can cause cancer — not your personal risk at a given exposure.
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The full explanation.
The simple version
Arsenic is a natural element found in soil, water, and air. It comes in two forms, and the inorganic form is the more toxic one. It can build up in drinking water, especially in private wells. Over many years, that exposure can cause cancer. Testing and treating your water is the main way to protect yourself.
What arsenic is
Arsenic occurs naturally in air, water, and soil. Mining and metal smelting can release it into the environment, and so can some farming processes. In parts of the United States and other countries, groundwater is naturally high in inorganic arsenic.
How people are exposed
Common ways people come into contact with it:
- Drinking water that is contaminated with arsenic.
- Smoking tobacco, or being around tobacco smoke.
- Eating food from plants watered with contaminated water.
- Older pesticides and medicines. Arsenic pesticides were widely used until the mid-1900s. Some medicines contained arsenic until the 1970s.
Arsenic in drinking water is generally thought to be more harmful than arsenic in food.
The cancer connection
Drinking arsenic-contaminated water for years is linked to bladder cancer and skin cancer. Medical exposure to arsenic has been clearly tied to skin cancer in population studies. Cancers of the lung, digestive tract, liver, kidney, and the blood and lymph systems have also been linked to arsenic.
The International Agency for Research on Cancer (IARC) studies the causes of cancer on behalf of the World Health Organization. It places arsenic in Group 1, carcinogenic to humans. That is the strongest evidence category. It means there is enough evidence that arsenic can cause cancer in people. The US National Toxicology Program agrees, listing arsenic in its Report on Carcinogens as known to be a human carcinogen.
Hazard is not the same as risk
Hazard and risk are not the same word. Calling arsenic a carcinogen is a claim about hazard. It means arsenic can cause cancer under some conditions. Your own risk is a separate question. It depends on the dose you take in, how long you take it in, and other factors. Two agents in one group can carry very different real-world risks. A listing answers "can it cause cancer?" It leaves "how likely is it for me?" open.
How to lower your exposure
Safe water for drinking, cooking, and watering food crops is the most important step.
- Test private well water for arsenic. Public systems must meet the EPA limit of 10 parts per billion.
- If levels are high, treat the water or switch to a safer source.
- Do not smoke, and stay away from secondhand smoke.
- Follow safety rules if you work around arsenic.
Any one exposure is easier to judge in context. Our overview of cancer prevention and what raises cancer risk give you that context.
The bottom line
Arsenic is a known human carcinogen (IARC Group 1). Your water supply is the piece you can most easily check and fix. Test a private well, treat it if levels are high, and then move on. A single label is not worth losing sleep over.
Words to know
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Common questions
Does arsenic cause cancer?
Yes. Arsenic is classified as a known human carcinogen, which means there is strong evidence it can cause cancer in people. 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 arsenic?
Most exposure happens by drinking water contaminated with inorganic arsenic, especially from private wells.
Which cancers are linked to arsenic?
It is most strongly linked to bladder, skin, and lung cancers.
How can I reduce my exposure to arsenic?
The main steps are testing well water and treating or switching to a safer source.
Does a carcinogen label mean I will get cancer?
No. A classification is about hazard — whether arsenic 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: 2026-08-11Next planned review: 2028-07-05
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How this page was created
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. We do not employ clinicians and do not intend to — our work 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 checked line by line against the sources listed on it. That confirms the sources support what the page says. 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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