Understanding Cancer Risk Factors

The simple versionExplain▾

It is usually not possible to know exactly why one person develops cancer and another does not. But research has shown that certain risk factors may increase a person's chance of developing cancer. There are also factors linked to a lower risk of cancer. These 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 factorExplain▾

Cancer risk factors include exposure to chemicals or other substances, as well as certain behaviors. They also 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 — a condition caused by inherited genetic changes that can lead to cancer.

Some of the most-studied known or suspected risk factors for cancer include:

• Age
• Alcohol
• Cancer-causing substances
• Chronic inflammation
• Diet
• Hormones
• Immunosuppression
• Infectious agents
• Obesity
• Radiation
• Sunlight
• Tobacco

Although some of these risk factors can be avoided, others — such as growing older — cannot.

Having a risk factor is not a diagnosisExplain▾

Having one or more risk factors does not mean a person will develop cancer. And cancer can develop in some people who do not have any known risk factors. Risk factors change the odds, but they do not decide what will happen to any one person.

In short: risk factors raise the chances, but they are not certainties.

How scientists study risk factorsExplain▾

Most cancer risk factors and protective 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. These studies may show that people who develop cancer are more or less likely to behave in certain ways, or to be exposed to certain substances, than people who do not.

On their own, such studies cannot prove that a behavior or substance causes cancer. For example, the finding could be a result of chance, or the true risk factor could be something other than the one suspected. Findings like these sometimes get attention in the media, which can lead to wrong ideas about how cancer starts and spreads.

When many studies point to a similar link between a possible risk factor and an increased risk of cancer, and when there is a possible explanation for how the factor could cause cancer, scientists can be more confident about the connection.

What this means for youExplain▾

Limiting your exposure to avoidable risk factors may lower your risk of developing certain cancers. But because some risk factors cannot be changed, and because cancer can happen with no known risk factors at all, 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 and any steps that make sense for you.