The short answer
A risk factor is anything that may increase a person's chance of getting cancer. Some risk factors, like age and family history, cannot be controlled, while others, like certain exposures and behaviors, can. Having a risk factor does not mean you will get cancer, and some people get cancer without any known risk factors.
A risk factor is anything that may increase a person's chance of developing cancer.
Risk factors include exposures, behaviors, and things people cannot control, like age and family history.
Some factors are linked to a lower risk of cancer; these are called protective factors.
Having a risk factor does not mean a person will get cancer, and cancer can occur with no known risk factors.
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This page is for anyone who wants to understand what a cancer risk factor is. It covers the main known risk factors, what having one does and does not mean, and how scientists study them.
The simple version
It is usually not possible to know exactly why one person gets cancer and another does not. But research has shown that certain risk factors may raise a person's chance of getting cancer. Other factors are linked to a lower risk. Those are sometimes called protective risk factors, or just protective factors.
In short: a risk factor is anything that may raise your chance of getting cancer.
What counts as a risk factor
Cancer risk factors include contact with chemicals or other substances. They also include certain behaviors. And they include things people cannot control, like age and family history.
A family history of certain cancers can be a sign of an inherited cancer syndrome. That is a condition caused by inherited genetic changes that can lead to cancer.
Some of the most-studied known or suspected risk factors for cancer are:
- Age
- Alcohol
- Cancer-causing substances
- Chronic inflammation
- Diet
- Hormones
- Immunosuppression (a weakened immune system)
- Infectious agents (germs such as some viruses)
- Obesity
- Radiation
- Sunlight
- Tobacco
Some of these can be avoided. Others, such as growing older, cannot.
Having a risk factor is not a diagnosis
Having one or more risk factors does not mean a person will get cancer. And cancer can develop in people with no known risk factors at all. Risk factors change the odds. They do not decide what happens to any one person.
In short: risk factors raise the chances, but they are not certainties.
How scientists study risk factors
Most risk factors and protective factors turn up first in epidemiology studies. In these studies, scientists look at large groups of people. They compare those who get cancer with those who do not. The studies may show a pattern. People who get cancer may be more or less likely to behave a certain way, or to have been exposed to a certain substance.
On their own, such studies cannot prove that a behavior or substance causes cancer. The finding could be due to chance. Or the true risk factor could be something other than the one suspected. Findings like these sometimes make headlines. That can spread wrong ideas about how cancer starts and spreads.
Confidence grows when many studies point the same way. It grows further when there is a plausible explanation for how the factor could cause cancer.
What this means for you
Limiting your contact with avoidable risk factors may lower your risk of certain cancers. But some risk factors cannot be changed. And cancer can happen with no known risk factors at all. So no one can promise that avoiding a risk factor will prevent cancer.
Your healthcare team is the best source of information about your own risk factors. They can also tell you which steps make sense for you.
Common questions
What is a cancer risk factor?
It is anything that may raise your chance of getting cancer. Examples include exposure to chemicals or other substances, certain behaviors, and things people cannot control, such as age and family history. Factors linked to a lower risk of cancer are sometimes called protective factors.
Does having a risk factor mean I will get cancer?
No. It is usually not possible to know exactly why one person develops cancer and another does not. Having one or more risk factors does not mean a person will get cancer, and cancer can develop in people who have no known risk factors.
How do scientists find cancer risk factors?
Most risk factors are first identified in epidemiology studies. In these studies, scientists look at large groups of people and compare those who develop cancer with those who do not. On their own, these studies cannot prove that a behavior or substance causes cancer, but confidence grows when many studies point to a similar link and a possible explanation exists.
Can a family history of cancer be a risk factor?
Yes. Cancer risk factors include things people cannot control, like age and family history. A family history of certain cancers can be a sign of a possible inherited cancer syndrome.
Can I lower my cancer risk?
Some risk factors can be avoided and others cannot. Limiting your exposure to avoidable risk factors may lower your risk of developing certain cancers. Your healthcare team can help you understand which of your risk factors can be changed.
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Sources last checked: 2026-07-21 what this meansLast updated: 2026-08-10Next planned review: 2027-07-21
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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, 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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