The main risk factors behind colorectal cancer

Colorectal cancer develops when cells in the colon or rectum grow abnormally and form tumors. Most cases start as small, noncancerous growths called polyps that can turn into cancer over years if not removed. The risk rises with age, family history, certain genetic conditions, inflammatory bowel disease, obesity, smoking, heavy alcohol use, and a diet high in red or processed meat. No single cause explains every case—most people with risk factors never develop the disease, and some without obvious risk factors do.

Understanding what increases your risk does not mean you will get colorectal cancer. It means you and your doctor can make informed decisions about screening timing, how often to screen, and whether genetic testing makes sense for your situation.

Key Takeaways

  • Age is the strongest risk factor—most colorectal cancers occur in people over 50, though rates in younger adults are rising.
  • A family history of colorectal cancer or polyps, or a personal history of inflammatory bowel disease, significantly raises risk.
  • Lifestyle factors including smoking, heavy drinking, obesity, and a diet heavy in red or processed meat contribute to cancer development.
  • Inherited genetic syndromes like Lynch syndrome and familial adenomatous polyposis account for a smaller share of cases but carry very high risk.
  • Screening can detect and remove polyps before they become cancer, which is why regular screening is the most effective prevention tool available.

Age and family history as the strongest predictors

Age is the single strongest risk factor. About 90 percent of colorectal cancers occur in people age 50 and older. The risk rises sharply after age 60. This is why screening guidelines recommend that people at average risk begin screening at age 45 to 50, depending on the organization and your doctor's assessment.

Family history matters significantly. If a parent, sibling, or child had colorectal cancer or polyps, your risk is higher—especially if they were diagnosed before age 50 or if multiple relatives were affected. The closer the relative and the younger they were at diagnosis, the higher your risk. If you have a family history, tell your doctor before your first screening; they may recommend starting earlier or screening more often than standard guidelines suggest.

Some families carry inherited genetic mutations that cause colorectal cancer at much higher rates. 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. Familial adenomatous polyposis (FAP) is rarer but even more serious—people with FAP develop hundreds or thousands of polyps in the colon and rectum and have nearly 100 percent risk of cancer by age 40 if the colon is not removed. Genetic testing can identify these syndromes, and if you have one, your doctor will recommend more frequent screening or preventive surgery.

Inflammatory bowel disease and polyp history

People with ulcerative colitis or Crohn's disease have a higher risk of colorectal cancer than the general population. The longer you have had inflammatory bowel disease and the more of the colon it affects, the higher your risk. This is why people with these conditions typically begin screening earlier than age 50 and may screen more frequently. Effective treatment of the underlying inflammation can lower cancer risk.

A personal history of polyps also raises risk. If you have had polyps removed, your doctor will recommend follow-up colonoscopies at intervals based on the type, size, and number of polyps found. Some polyps are more likely to become cancer than others. Adenomatous polyps carry the highest risk; hyperplastic polyps carry very little. Your pathology report will specify what was removed, and your doctor will use that information to set your screening schedule.

Lifestyle factors that increase risk

Obesity is linked to higher colorectal cancer risk in both men and women. The relationship appears to involve inflammation, insulin resistance, and changes in hormone levels. Maintaining a healthy weight through diet and physical activity may lower your risk.

Smoking and heavy alcohol use both raise colorectal cancer risk. Smokers have a higher risk than nonsmokers, and the risk increases with years of smoking. Heavy alcohol consumption—typically defined as more than one drink per day for women or two for men—is associated with increased risk. Quitting smoking and limiting alcohol can reduce this risk over time.

Diet plays a role. Diets high in red meat (beef, pork, lamb) and processed meat (bacon, sausage, deli meats, hot dogs) are associated with higher colorectal cancer risk. The mechanisms are not fully understood but may involve carcinogens formed during cooking or processing, or changes in gut bacteria. Conversely, diets high in fiber, vegetables, fruits, and whole grains are associated with lower risk. Physical inactivity also raises risk; regular exercise appears protective.

How polyps develop into cancer

Most colorectal cancers begin as polyps—small growths on the inner lining of the colon or rectum. Not all polyps become cancer, and the process usually takes many years. A polyp may grow slowly for 10 to 15 years before becoming cancerous. This long timeline is why screening is so effective: finding and removing polyps before they turn into cancer prevents most colorectal cancers.

Polyps form when cells in the colon lining divide abnormally. Over time, genetic mutations accumulate in these cells. The adenoma-carcinoma sequence describes this step-by-step progression: a normal cell develops a mutation, becomes a small polyp, accumulates more mutations, grows larger, and eventually becomes invasive cancer. This sequence is not inevitable—many polyps never progress—but the longer a polyp sits, the higher the chance it will eventually become cancer.

Genetic mutations and how they work

Colorectal cancer develops when cells accumulate mutations in genes that normally control cell growth and division. The most commonly mutated genes in colorectal cancer are APC, KRAS, and TP53. These genes act as brakes on cell division or as repair systems for damaged DNA. When they are mutated, cells can divide without control and ignore signals to stop growing or die.

Most of these mutations happen randomly during a person's lifetime and are not inherited. However, some people inherit a mutation in one of these genes from a parent, which means every cell in their body carries that mutation from birth. This dramatically increases their risk. People with Lynch syndrome inherit a mutation in one of several DNA repair genes. People with FAP inherit a mutated APC gene. Genetic counseling and testing can identify these inherited mutations, and if you carry one, your doctor will recommend intensive screening or preventive measures.

Race, ethnicity, and other demographic factors

Colorectal cancer incidence and outcomes vary by race and ethnicity in the United States. Black Americans have the highest incidence and mortality rates from colorectal cancer. This difference is driven by a combination of factors: later-stage diagnosis at the time of screening, differences in access to high-quality screening and treatment, higher rates of certain risk factors like smoking and obesity, and possibly biological differences in tumor behavior. American Indian and Alaska Native populations also have higher incidence rates.

Hispanic and Asian American populations have lower incidence rates than non-Hispanic white populations, though rates are rising in younger Hispanic Americans. These patterns reflect differences in screening rates, risk factor prevalence, and healthcare access rather than inherent biological differences between groups. Ensuring equitable access to screening and treatment is an important public health goal.

Frequently Asked Questions

Can you get colorectal cancer without any risk factors?

Yes. While risk factors increase the likelihood, colorectal cancer can develop in people with no family history, no polyps, no inflammatory bowel disease, and no lifestyle risk factors. This is why screening is recommended for all adults at average risk starting at age 45 to 50, regardless of whether they have identifiable risk factors.

Does having a risk factor mean I will definitely get colorectal cancer?

No. Many people with risk factors never develop colorectal cancer. Risk factors increase the probability, but they do not may provide the disease will occur. This is why your doctor considers your full risk profile when deciding when to start screening and how often to screen.

If my parent had colorectal cancer, when should I start screening?

Talk to your doctor. General guidelines suggest starting at age 40 to 45 if a parent was diagnosed before age 50, or at age 50 if they were diagnosed at 50 or older. Your doctor may recommend earlier or more frequent screening based on your specific family history and other factors.

Does diet alone prevent colorectal cancer?

Diet is one factor among many. A healthy diet high in fiber and vegetables and low in red and processed meat may lower risk, but it cannot eliminate it, especially if you have other risk factors like family history or inflammatory bowel disease. Screening remains the most effective way to prevent colorectal cancer by detecting and removing polyps before they become cancer.

Are younger people getting colorectal cancer more often now?

Yes. Colorectal cancer rates in adults under 50 have been rising over the past two decades, particularly in people in their 40s. The reasons are not fully understood but may involve changes in diet, obesity rates, physical activity, and the microbiome. This trend is one reason screening guidelines have shifted to recommend starting at age 45 rather than 50 for average-risk adults.