Here’s what we understand about the causes of colorectal cancer, what’s known about colorectal cancer risk factors, and how to modify your personal risk profile.

What causes colorectal cancer?

Colorectal polyps and cancer can develop when something goes wrong in the normal and necessary processes through which the inner lining of the colon is renewed, a process known as cell division.

In the lining of the colon, cells are constantly aging, dying, and being replaced by new cells. Every time cells divide anywhere in the body, including those lining the inner surface of the colon and rectum, there is a risk that the process can go wrong. Errors in building the DNA that governs the processes needed to maintain cells can lead to uncontrolled cell division.

Every time a cell divides, its DNA must be rebuilt, and cells are constantly dividing in the body. In some cases, newly formed cells are so abnormal, they don’t survive. In other cases, abnormal cells start to multiply in an uncontrolled way. This process can lead to a buildup of abnormal cells.

In the colon or rectum, these growths are called polyps. These polyps can be benign, precancerous, or malignant (cancerous).

What causes abnormal cells to develop?

This is a complex process that is not completely understood. There are conditions that are inherited or influenced by environmental factors that are known to increase or decrease a person’s risk of developing polyps of colorectal cancer. These are known as risk factors.

Risk factors don’t necessarily cause colorectal cancer, but they can increase the likelihood that cell division can go awry. Just because you have a risk factor, it doesn’t mean you will necessarily get cancer.

However, by knowing if you carry risk factors or have environmental exposures that are associated with an increased risk of cancer, you can be proactive about managing your health by making changes in your environment or behavior (when possible), and by setting up screening routines that based upon your individual risk profile.

What’s your risk? Take our Colorectal Cancer Screening Quiz to find out.

What are the colorectal cancer risk factors?

Age

Age is one of the top risk factors for colorectal cancer. As our bodies get older, the likelihood that errors will occur in the process of cell division goes up. Although the frequency of colorectal cancer in young adults is increasing, colorectal cancer is most frequently diagnosed in older people. The median age of diagnosis is 66.

Simply put: The older you get, the higher your risk of colorectal cancer.

If you are 45 or older, your risk for colorectal cancer is increased simply on the basis of your age. Currently, the recommendation from a number of agencies that study the risks and benefits of screening tests for individuals and for society agree that you need regular screening starting at age 45.

Family History

Colorectal cancer can run in families. If one of your first-degree, biological relatives has been diagnosed with colorectal cancer and/or colon polyps, your risk is also increased. First-degree relatives include parents, siblings, and offspring.

As many as 1 in 3 colorectal cancer patients report that a biological family member has also had the disease. The causes of this may be a blend of both inherited genes that predispose individuals to develop cancers and to environmental factors.

If the family member with colorectal cancer was under age 50 at the time of diagnosis, or if multiple family members have been diagnosed with colorectal cancer, the risk for their relatives is even higher than if only one relative or only an older relative has had the disease.

Did the doctor find polyps? Tell your family.

Family history doesn’t only apply to relatives who carry a cancer diagnoses: If a first-degree relative has also had a polyp found and removed, that can also increase your risk of having the same thing happen.

Not all types of colorectal polyps increase the risk of developing cancer, and it is important to understand exactly what kind of polyp was removed. Your doctor can help you to understand when polyps indicate a higher risk of developing colorectal cancer or when they are not precancerous.

It’s important to discuss your family history with your doctor and, when a risk factor is identified, to share your cancer history with your family and let them know your screening results as well. Sharing health information among family members can save lives.
Discovering your family’s health history is an important step in managing your and your relative’s colorectal cancer risk.

Personal history of polyps

If you have undergone a colonoscopy and been told you have large or advanced polyps in your colon or rectum, you are at an increased risk for developing colorectal cancer. If polyps are found and cannot be removed during the colonoscopy, they can turn into cancer. Sometimes surgery is needed to remove polyps.

Once you’ve discovered that you have a polyp, your risk to develop polyps in the future is elevated. You need to stay on schedule with the colorectal cancer screening plan your doctor outlines for you.

Advanced polyps are often referred to as premalignant or precancerous, and these have a high risk of turning into cancer if not removed.

A colonoscopy is the only colorectal cancer screening tool that will identify a polyp and allow it to be removed in the same procedure before it turns into cancer. Other screening tests, such as Cologuard (a stool test), or CT colonography (an x-ray) can identify polyps, but a colonoscopy will be needed to remove them.

Personal history of inflammatory bowel disease

If you’ve been diagnosed with inflammatory bowel disease (IBD)—like Crohn’s disease or ulcerative colitis—you are at an increased risk for colorectal cancer. IBD tends to damage and cause inflammation in the inner lining of the colon and rectum, and inflammation can create an environment for abnormal cells to grow.

You’re likely working with a gastroenterologist already if you’ve been diagnosed with IBD, so discuss your increased risk of colorectal cancer and an appropriate screening schedule for you.

Personal history of cancer

If you’ve been previously diagnosed with breast cancer, ovarian cancer, uterine cancer, pancreatic cancer, or colorectal cancer, your risk of having another cancer, including colorectal cancer, is increased.

If you’ve had prior radiation therapy on your abdomen or pelvis to treat a prior cancer, this also increases your risk of developing another cancer, including colorectal cancers.

It’s important to stick to your follow-up plan (also called surveillance) set by your doctor to monitor and prevent future cancer cases.

Your risk of developing another cancer is higher if you were younger when you were diagnosed with the first cancer.

Type 2 Diabetes

People with type 2 diabetes are at an increased risk for colorectal cancer. Many of the lifestyle factors that lead to type 2 diabetes, such as being overweight and leading a sedentary lifestyle, also contribute to an increased risk of colorectal cancer, and the disease itself may also impact a patient’s colorectal cancer prognosis.

Physical Health and Wellness

Your lifestyle, diet, and physical activity all play into colorectal cancer risk. Studies have shown that being overweight or obese is a risk factor, especially in men, for colorectal cancer. Lack of physical activity also increases your colorectal cancer risk. Regular exercise has been proven to lower risk.

Read our fact sheet: Exercise and colorectal cancer

What you eat, drink, and smoke can put you at a higher risk for colorectal cancer:

• Little fruit, vegetable, grains, and fiber in your diet
• Low vitamin D
• Smoking tobacco
• Heavy alcohol use (more than one drink a day for women and two drinks a day for men)
• A diet high in red meat (beef, pork, lamb), processed meats (hot dogs, sausage, lunch meats), and fats
• A diet that includes a lot of sugary drinks
• Meat preparation methods that includes frying, grilling, broiling, or other methods of cooking that use very high temperatures that can lead to charring of the surface of the food

Race, Ethnicity, and Gender

The following racial groups in the United States are getting diagnosed and passing away at higher rates compared to other ethnicities:

• Alaska Native People
• American Indians
• African Americans
• Young Hispanics

Worldwide, Jews of Eastern European descent (Ashkenazi Jews) may have the highest risk of colorectal cancer.

While both men and women can get colorectal cancer, it’s more commonly diagnosed in men, and men more often die from the disease.

Doctors may suggest earlier screening if your race and ethnicity present an increased risk.

Read more about race and ethnicity risks:

• CDC: Colorectal Cancer by Age, Sex, Race and Ethnicity
• SEER: Cancer Stat Facts: Colorectal Cancer
• ACS: Colorectal Cancer Statistics 2023

Genetic Syndromes

If you have been diagnosed with a hereditary colorectal cancer syndrome, you are at high risk for colorectal cancer. About 5% of colorectal cancer patients have a hereditary cancer syndrome.

Individuals and their family members with these syndromes need intensive and early screening for colorectal and potentially other cancers. These intensive approaches can detect precancerous growths or detect cancers in their early stages—when they are most likely to be curable.

The most common genetic syndromes include:

• Lynch syndrome (or HNPCC) (2%-4% of all colorectal cancers)
• Familial adenomatous polyposis (FAP) (1% of all colorectal cancers)

Although rarer, the following genetic syndromes also put you at a high risk of colorectal cancer:

• Peutz-Jeghers syndrome (PJS)
• MUTYH-associated polyposis (MAP)
• Cystic fibrosis (CF)

Is everyone at risk?

Everyone who has a colon is at risk for colorectal cancer, but everyone’s risk level is different.

What are the colorectal cancer risk levels?

Average risk

Your risk for colorectal cancer is similar to that of the general U.S. population.

Approximately 1 in 20 people with average risk will develop colorectal cancer in their lifetimes.

However, screening and lifestyle choices can reduce this risk. Guidelines recommend that people of average risk begin screening at age 45.

Increased risk

You should talk to your provider about their preferred screening schedule and screening methods for your situation.

High risk

If you have a first-degree relative with a history of colorectal cancer, you should be begin screening 10 years before the age of the diagnosis of your youngest relative with colorectal cancer, or at age 40, whichever comes first. Talk to your provider about when you should begin screening if you have a personal history of inflammatory bowel disease of the colon, or a personal or family history of large or advanced polyps in your colon or rectum.

Hereditary risk

You should speak to your physician about hereditary cancer risk for yourself and your family and consider meeting with a genetic counselor.

What can I do to lower my risk?

Some risk factors—like race, ethnicity, and personal or family history of cancer or polyps—cannot be changed. This is why it’s important to know your risk and create a screening plan with your doctor. However, some risk factors can be improved.

Stop smoking.

Eat a diet full of fruits, vegetables, and fiber. Avoid a diet full of processed meats and red meats. One recommended diet is commonly called a “Mediterranean diet” and many cookbooks and websites can help you understand how to follow it.

Exercise that lowers risk can take many forms, and aerobic exercise should be a part of any plan. Aerobic exercise can include walking, running, hiking, biking, swimming, and many other activities. Research suggests that 120 minutes or more of aerobic exercise per week reduces health risks, including the risk of developing colorectal cancer.

Don’t drink alcohol—or if you choose to drink, limit your intake to one or two drinks per day or less.

Check your vitamin D levels to ensure you’re not deficient and take supplements if your levels are low.

These are steps that won’t only make you healthier overall, but they’ll lessen your colorectal cancer risk, too.