Rectal cancer does not come from one single cause or action, and there is no safe or “guaranteed” way to get it on purpose. It develops over many years from changes in cells in the lining of the rectum, often starting as small benign polyps that may slowly turn cancerous.

How rectal cancer develops

Rectal cancer starts when cells in the rectum’s lining acquire DNA mutations that make them grow and divide out of control instead of dying when they should. These abnormal cells can form polyps, and some polyps gradually become cancer over about 10–15 years. In most people, this is a slow, silent process with no symptoms at first, which is why screening colonoscopies are so important.

Main risk factors (things that raise the chance)

You cannot “aim” to get rectal cancer, but certain factors make it more likely over a lifetime.

  • Age over 50 (though cases in younger adults have been rising).
  • Personal or family history of colorectal polyps or colorectal cancer.
  • Chronic inflammatory bowel disease (ulcerative colitis, Crohn’s disease).
  • Certain inherited syndromes (Lynch syndrome, familial adenomatous polyposis).
  • Diet high in red and processed meats and low in fiber.
  • Obesity, physical inactivity, and type 2 diabetes.
  • Smoking and heavy alcohol use.

These do not guarantee cancer; they only increase risk, and many people with rectal cancer have no obvious risk factor.

Quick HTML table of key risk factors

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Risk factor How it influences rectal cancer risk
Age > 50 Most rectal and colon cancers are diagnosed after age 50.
Family history / polyps Close relatives with colorectal cancer or polyps significantly raise lifetime risk.
Inflammatory bowel disease Long-standing ulcerative colitis or Crohn’s disease in the colon/rectum increases risk.
Inherited syndromes Lynch syndrome and familial adenomatous polyposis cause very high polyp and cancer risk.
Diet high in red/processed meat Associated with higher colorectal cancer rates, especially with low fiber intake.
Obesity & inactivity Linked to higher colorectal cancer risk and worse outcomes.
Smoking & heavy alcohol use Increase the likelihood of polyps and malignant transformation.

Symptoms to watch for (and not ignore)

People often discover rectal cancer because of symptoms, not because they “caused” it.

Common warning signs include:

  • Blood in the stool, dark or bright red rectal bleeding.
  • Change in bowel habits lasting more than a few weeks (diarrhea, constipation, thinner stools).
  • Feeling like the bowel doesn’t fully empty.
  • Unexplained weight loss or fatigue.
  • Abdominal discomfort or pain.

If you have any of these, especially rectal bleeding, you should see a doctor promptly rather than trying to self-diagnose.

What you can do to lower risk (the opposite of “how to get it”)

If your question comes from fear, curiosity, or something you read online, it may help to focus on protection instead of causation.

Steps that can help lower risk over time:

  1. Get age-appropriate colorectal screening (often starting at 45, sometimes earlier with strong family history).
  1. Stay physically active and maintain a moderate weight.
  1. Eat more fruits, vegetables, whole grains, and less processed/red meat.
  1. Avoid smoking and limit alcohol.
  1. If you have inflammatory bowel disease or a genetic syndrome, follow your specialist’s schedule for colonoscopies and checkups.

If you’re worried right now

If your question was triggered by current symptoms or a family member’s diagnosis, you are not alone, and worrying does not mean you did something wrong. Rectal cancer is common, highly studied, and often very treatable when found early. Talking with a healthcare professional (or encouraging your loved one to) is the best next step.

Information gathered from public forums or data available on the internet and portrayed here.