The short answer
Screening tests are designed to find cancer early, when it is often easier to treat. Mammograms use a low dose of x-rays, and experts say the benefits outweigh the possible harm. A CT scan adds a small cancer risk from radiation. A colonoscopy uses no radiation and can remove polyps before they turn into cancer.
Screening tests are made to find disease early, not to cause it.
A typical screening mammogram gives about 0.4 mSv of radiation, about the same as 1 to 2 months of radiation from normal, everyday life.
Radiation from CT scans raises cancer risk a little, but the risk from one scan is small.
Colonoscopy uses no radiation, and doctors can remove polyps during the test.
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The simple version
Screening tests are made to find disease early, often before any symptoms show up. Some people online say that tests like mammograms, CT scans, and colonoscopies cause cancer. The evidence does not support that. Some tests use a small amount of radiation, and that adds a small risk. Experts say that for recommended tests, the benefits outweigh that risk.
Screening is built to find cancer, not cause it.
Mammograms
A mammogram is an x-ray picture of the breast. NCI describes it as an imaging test that uses low-dose x-rays. A diagnostic mammogram, used to look into a problem, uses a higher dose than a screening mammogram.
The American Cancer Society says a typical screening mammogram, with two views of each breast, gives about 0.4 mSv of radiation. That is about the same as the radiation a person gets from normal, everyday life over 1 to 2 months. ACS says the benefits of breast cancer screening outweigh any possible harm from that radiation.
The dose is low, and experts say it is worth it.
CT scans
A CT scan takes many x-ray pictures to build a detailed view of the inside of the body. NCI says ionizing radiation is known to raise cancer risk. That is a real fact, not a myth. But NCI also says the added risk from one CT scan is still small.
To give a sense of scale, NCI says:
- A low-dose chest CT (about 1.5 mSv) is like 6 months of natural background radiation.
- A typical chest CT (about 6.1 mSv) is like 2 years of natural background radiation.
Children are more sensitive to radiation because their bodies are still growing. NCI describes a large study that found about 1 to 2 extra blood cancers for every 10,000 CT scans given to young people, in the 12 years after the scan. The scans in that study were given before age 22.
NCI says that when a CT scan is used to diagnose cancer or another serious condition in someone with symptoms, the benefits greatly outweigh any possible risks.
CT radiation is a small risk, and it is weighed against a real need.
Colonoscopy
A colonoscopy uses a thin, flexible tube with a light and a tiny camera. It does not use radiation. The American Cancer Society notes a small risk of bleeding, bowel tears, or infection.
During the test, doctors can take samples or remove polyps. Polyps are small growths, and some can turn into cancer over time. Removing them is one of the main benefits of the test.
A different test, called CT colonography, looks at the colon with a CT scan. It does use a small amount of radiation.
A colonoscopy can help prevent cancer, not cause it.
What about sterilizing chemicals?
Some posts say the tools used in tests like Pap smears are cleaned with a chemical that causes cancer. The FDA says about half of sterile medical devices in the U.S. are sterilized with a gas called ethylene oxide. For many devices, it is the only method that works without damaging them.
Long exposure to ethylene oxide has been linked to cancer. Recognized voluntary standards set acceptable limits on how much can be left on a device, and the FDA reviews makers' sterility information against the standards it recognizes.
Every test has trade-offs
No medical test is risk-free. Screening can also lead to false alarms or extra tests. That is why it helps to talk with your care team about which tests make sense for your age, health, and family history.
If you notice a change in your body that is new or lasts, get it checked, even if you are up to date on screening. In an emergency, call 911 or go to the nearest emergency room.
Common questions
Do mammograms cause breast cancer?
Mammograms use low-dose x-rays. The American Cancer Society says a typical screening mammogram gives about 0.4 mSv, and that the benefits of breast cancer screening outweigh any possible harm from the radiation.
Can a CT scan give me cancer?
Ionizing radiation is known to raise cancer risk, and CT scans use it. NCI says the added risk from one CT scan is still small. When a scan is used to diagnose a serious condition, NCI says the benefits greatly outweigh the risks.
Are children more at risk from CT scans?
Yes, a bit. NCI says children are more sensitive to radiation than adults. One large study found about 1 to 2 extra blood cancers for every 10,000 CT scans given to young people. Ask your child's doctor why a scan is needed.
Does a colonoscopy use radiation?
No. A colonoscopy uses a thin, flexible tube with a light and camera. The American Cancer Society notes a small risk of bleeding, bowel tears, or infection. A different test, CT colonography, does use a small amount of radiation.
Are medical tools sterilized with chemicals that cause cancer?
The FDA says about half of sterile medical devices in the U.S. are sterilized with ethylene oxide. Long exposure to it has been linked to cancer, so recognized voluntary standards set limits on how much can be left on a device, and the FDA reviews makers' sterility information against the standards it recognizes.
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Last updated: 2026-09-27Next planned review: 2027-09-27
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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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