The main risk factors for rectal cancer

Rectal cancer develops when cells in the lining of the rectum grow abnormally and form a tumor. Most rectal cancers start as growths called polyps, which can turn into cancer over time if not removed. The risk goes up with age—most people diagnosed are over 50—but younger people can develop it too.

No single cause explains every case. Instead, rectal cancer usually results from a combination of factors: inherited genes, lifestyle habits, medical history, and sometimes just chance. Understanding what raises your risk helps you know when screening matters and what changes might lower your chances.

Key Takeaways

  • Age over 50, a family history of colorectal cancer, and inflammatory bowel disease are the strongest risk factors for rectal cancer.
  • Smoking, heavy alcohol use, obesity, and a diet high in red meat and processed foods increase rectal cancer risk.
  • Inherited genetic conditions like Lynch syndrome and familial adenomatous polyposis cause rectal cancer in some families at much younger ages.
  • Screening with colonoscopy can find and remove polyps before they become cancer, which is why it is recommended starting at age 45 to 50 for most people.
  • Having one risk factor does not mean you will develop rectal cancer, but multiple factors together raise the odds.

Age and family history as the strongest predictors

Age is the single biggest risk factor. About 90 percent of rectal cancer cases occur in people 50 and older. The disease is rare in people under 40, but it does happen, and rates in younger adults have been rising over the past two decades for reasons doctors are still studying.

Family history matters significantly. If a parent, sibling, or child had colorectal cancer before age 50, your risk is higher. If multiple family members had it, or if someone had it at a young age, your risk climbs further. Genetic testing may be worth discussing with your doctor if your family pattern is strong.

Inherited genetic conditions that sharply raise risk

Lynch syndrome (also called hereditary nonpolyposis colorectal cancer, or HNPCC) accounts for 2 to 4 percent of all colorectal cancers. People with Lynch syndrome have a 70 to 80 percent lifetime risk of developing colorectal cancer, often in their 40s or 50s. The condition is caused by a mutation in one of several DNA repair genes passed down through families.

Familial adenomatous polyposis (FAP) is rarer but more severe. People with FAP develop hundreds or thousands of polyps in the colon and rectum starting in their teens or 20s. Without surgery to remove the colon, nearly 100 percent will develop colorectal cancer by age 40. A genetic test can identify FAP, and family members can be screened.

If you have a strong family history of colorectal cancer or polyps, ask your doctor whether genetic testing or earlier screening makes sense for you. Knowing you carry one of these mutations changes when and how often you should be screened.

Inflammatory bowel disease and chronic inflammation

People with ulcerative colitis or Crohn's disease have a higher risk of developing colorectal cancer, including rectal cancer. The longer you have had the disease and the more of the colon it affects, the higher the risk. The chronic inflammation in the bowel appears to damage cells over time and make them more likely to become cancerous.

If you have inflammatory bowel disease, your doctor will likely recommend colonoscopy screening more often than the standard schedule—sometimes every one to two years rather than every 10 years. Staying on medication that controls inflammation may also lower your cancer risk.

Lifestyle factors that increase risk

Smoking raises rectal cancer risk. The longer and heavier someone smokes, the higher the risk. Quitting reduces risk over time, though it takes years for the benefit to fully appear.

Alcohol use, especially heavy drinking, is linked to higher rectal cancer risk. The relationship appears to be dose-dependent—more drinking means more risk.

Obesity increases the risk for both men and women. The excess weight may affect hormone levels and inflammation in ways that promote cancer growth.

Diet plays a role. Eating a lot of red meat (beef, pork, lamb) and processed meat (bacon, sausage, deli meat, hot dogs) is associated with higher risk. A diet low in fiber, fruits, and vegetables is also linked to increased risk. The opposite pattern—more fiber, more vegetables, more whole grains—appears protective.

Physical inactivity is another factor. People who exercise regularly have lower rectal cancer risk than those who are sedentary.

Other medical conditions and treatments

Type 2 diabetes is associated with a modestly higher rectal cancer risk, possibly because of shared risk factors like obesity and diet, or because of how diabetes affects hormone and inflammation levels.

Previous radiation to the pelvis—for treatment of another cancer, for example—raises the risk of developing rectal cancer years later. The risk is highest 10 to 20 years after radiation.

Some studies suggest that hormone replacement therapy in postmenopausal women may lower rectal cancer risk, though the evidence is mixed and other health effects of hormone therapy must be weighed.

Why some people get rectal cancer with no known risk factors

Many people diagnosed with rectal cancer have few or no obvious risk factors. Cancer can develop by chance when cells divide and a random mutation occurs that leads to abnormal growth. This is why screening is recommended for everyone at average risk starting at age 45 to 50, not just people with risk factors.

Researchers continue to study why rectal cancer rates are rising in younger adults and what environmental or genetic factors may be involved. If you are concerned about your personal risk, your doctor can discuss your individual situation and recommend screening timing and methods that fit your circumstances.

Frequently Asked Questions

Does having one risk factor mean I will get rectal cancer?

No. Having a risk factor means the odds are higher than for someone without that factor, but most people with risk factors never develop rectal cancer. Risk is about probability, not certainty. Multiple risk factors together raise the odds more than a single one does.

Can rectal cancer be prevented?

You cannot eliminate risk entirely, but you can lower it. Quitting smoking, limiting alcohol, maintaining a healthy weight, exercising regularly, and eating a diet rich in fiber and vegetables all reduce risk. Regular screening and removal of polyps before they become cancer is the most effective prevention available.

At what age should I start getting screened?

Most organizations recommend starting at age 45 to 50 for people at average risk. If you have a family history of colorectal cancer, especially before age 50, or if you have inflammatory bowel disease or an inherited genetic condition, screening should start earlier. Ask your doctor what age and screening method is right for you.

If my parent had rectal cancer, will I definitely get it?

Not necessarily. Having a parent with rectal cancer increases your risk, but it does not may provide you will develop it. Your risk depends on the age at which your parent was diagnosed, whether genetic mutations run in your family, and your own lifestyle factors. Genetic testing can clarify whether you carry a hereditary mutation.

Does diet really make a difference in rectal cancer risk?

Yes. Eating less red and processed meat and more fiber, vegetables, and whole grains is linked to lower rectal cancer risk. The effect is modest compared to screening, but diet is one of the few risk factors you can control directly. Small changes add up over time.