Explainer
Colorectal cancer risk factors: what raises and lowers your risk
Colorectal cancer is cancer of the colon or rectum. Some risk factors, like age and family history, cannot be changed. Others, like alcohol, smoking and weight, can. Here is what the National Cancer Institute and MedlinePlus list, the symptoms to report, and when screening starts.
What colorectal cancer is
MedlinePlus, from the National Library of Medicine, explains that colorectal cancer develops in the tissues of the colon or rectum, the two parts of the large intestine. It happens when there are changes in your genetic material (DNA). Often these changes happen during your lifetime and the exact cause is unknown, but some changes that raise the risk are inherited. Lifestyle and the environment can also affect the risk (MedlinePlus).
Risk factors that raise the risk
The National Cancer Institute (NCI) lists these risk factors (NCI PDQ):
- Age. The risk increases after age 50, and most cases are diagnosed after age 50 (NCI PDQ).
- Family history. Having a parent, brother, sister or child with colorectal cancer doubles a person's risk (NCI PDQ).
- Personal history. A previous colorectal cancer, high-risk adenomas (polyps 1 centimeter or larger, or with cells that look abnormal under a microscope), ovarian cancer, or inflammatory bowel disease such as ulcerative colitis or Crohn disease (NCI PDQ). MedlinePlus names chronic ulcerative colitis or Crohn disease for 8 years or more (MedlinePlus).
- Inherited risk. Gene changes linked to familial adenomatous polyposis (FAP) or Lynch syndrome (hereditary nonpolyposis colon cancer) (NCI PDQ) (MedlinePlus).
- Alcohol. Drinking 3 or more alcoholic drinks a day raises the risk, and drinking is also linked to large colorectal adenomas (NCI PDQ). See alcohol and cancer risk.
- Cigarette smoking. Linked to a higher risk of colorectal cancer and of dying from it, and to adenomas (NCI PDQ).
- Race. Black people have a higher risk of colorectal cancer and of death from it compared to other races (NCI PDQ) (MedlinePlus).
- Obesity. Linked to a higher risk of colorectal cancer and of dying from it (NCI PDQ). To check your weight, use the BMI calculator.
Which ones you can change
| Risk factor | Can you change it? | Where to look here |
|---|---|---|
| Age | No | Colon cancer screening age |
| Family history | No | Colon cancer screening age (family history section) |
| Personal history, inherited syndromes | No | Talk to your provider about screening |
| Alcohol | Yes | Alcohol and cancer risk |
| Smoking | Yes | Quit smoking check |
| Obesity | Yes | BMI calculator |
What lowers the risk
- Physical activity. A lifestyle with regular physical activity is linked to a lower risk (NCI PDQ).
- Polyp removal. Most colorectal polyps are adenomas, which may turn into cancer. Removing polyps larger than 1 centimeter (pea-sized) may lower the risk; it is not known whether removing smaller polyps does. Possible harms of removal include a tear in the colon wall and bleeding (NCI PDQ).
- Aspirin. NCI says studies have shown that daily aspirin for at least two years lowers the risk of colorectal cancer and of dying from it, with the drop starting 10 to 20 years later. Its possible harms include a higher risk of stroke and of bleeding in the stomach and intestines (NCI PDQ). Do not start aspirin without talking to your provider; see the daily aspirin check.
NCI says it is not clear whether other NSAIDs, calcium supplements, or a diet low in fat and meat and high in fiber, fruits and vegetables lower the risk. Estrogen-only hormone therapy and statins do not affect it (NCI PDQ).
Symptoms to report
Colorectal cancer may not cause symptoms, especially at first. If there are symptoms, MedlinePlus lists (MedlinePlus):
- A change in bowel habits that lasts more than a few days, such as diarrhea, constipation, feeling that the bowel does not empty completely, or stool that is narrower or a different shape than usual
- Blood (bright red or very dark) in the stool
- Frequent gas pains, bloating, fullness or cramps
- Weight loss for no known reason
- Fatigue
Tell your provider about any of these. They have other causes too, and only tests can tell.
When screening starts
Because colorectal cancer may not cause symptoms at first, screening matters (MedlinePlus). The US Preventive Services Task Force recommends screening for adults from 45 to 75, and offering it selectively from 76 to 85 (USPSTF 2021). People at high risk should talk to their provider about how often and which test (MedlinePlus). The colon cancer screening age check walks through it, and the cancer risk calculator page shows the checks for other cancers.
Common questions
Does a family history mean I will get colorectal cancer?
No. A parent, brother, sister or child with colorectal cancer doubles the risk (NCI PDQ), which raises your chance but does not decide it. It can change when and how you are screened, so tell your provider.
Can I get colorectal cancer if I am under 50?
Yes. NCI says most cases are diagnosed after age 50, not all (NCI PDQ), and USPSTF screening starts at 45 (USPSTF 2021). Report symptoms at any age.
Sources
- PDQ Screening and Prevention Editorial Board. Colorectal Cancer Prevention (PDQ): Patient Version. National Cancer Institute. Updated May 2, 2025. www.cancer.gov/types/colorectal/patient/colorectal-prevention-pdq
- MedlinePlus (National Library of Medicine). Colorectal Cancer. Last updated March 5, 2024. medlineplus.gov/colorectalcancer.html
- US Preventive Services Task Force. Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement. JAMA. 2021;325(19):1965-1977. www.uspreventiveservicestaskforce.org/uspstf/recommendation/colorectal-cancer-screening
Written and maintained by the uncovermyrisk.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-11-05. Spotted an error? See About.