A rectal polyp is a small growth of tissue that forms on the inner lining of the rectum. Most rectal polyps are harmless and cause no symptoms, but certain types can slowly develop into cancer over many years if left in place. The rectum is actually the most common location for polyps in the entire colon, and screening colonoscopies find them frequently: about 42% of people under 50 and 76% of people 50 and older have at least one polyp detected during screening.
Types of Rectal Polyps
Not all polyps carry the same risk. The type of cells inside the polyp determines whether it could become a problem.
Adenomas are the polyps doctors pay the most attention to. These contain abnormal cells and are recognized as the precursor lesions for colorectal cancer. About 25% of people aged 50 and older have adenomas, and that number climbs to around 50% by age 70. Adenomas follow what’s called the adenoma-carcinoma sequence: normal tissue becomes an adenoma, and over years, the adenoma can accumulate enough genetic changes to become cancer.
Hyperplastic polyps were long considered completely harmless because their cells lack the obvious abnormalities seen in adenomas. They’re common, especially in the rectum, and most are small. The vast majority don’t progress to cancer.
Serrated polyps are a more recently understood category. Some polyps that were previously lumped in with hyperplastic polyps actually carry a real risk of progressing to cancer through a different biological pathway than adenomas. This group includes sessile serrated lesions and traditional serrated adenomas. They’re important because they can be harder to spot during a colonoscopy, as they tend to be flat and blend into the surrounding tissue.
What Rectal Polyps Look Like
Polyps vary in shape, and shape matters for how they’re removed. Pedunculated polyps hang from the intestinal wall on a stalk, like a mushroom. Sessile polyps sit flat against the wall without a stalk, making them harder to remove cleanly. Some polyps are completely flat or even slightly depressed below the surface of the surrounding tissue. Polyps range in size from a few millimeters (smaller than a pencil eraser) to several centimeters.
Symptoms You Might Notice
Most people with rectal polyps feel perfectly fine. You typically can’t tell you have them, which is exactly why screening matters so much.
When polyps do cause symptoms, rectal bleeding is the most common. You might notice blood on toilet paper, on your underwear, or mixed into your stool. Blood from rectal polyps can appear bright red or make stool look darker than usual. Over time, slow bleeding from a polyp can lead to iron deficiency anemia, which shows up as persistent fatigue and weakness. Some larger polyps produce mucus discharge or cause changes in bowel habits, but this is less common.
Risk Factors
Some risk factors for developing polyps are within your control, and some aren’t. Age is the biggest one: polyp rates nearly double after age 50. Gender and race also play a role, with higher rates in men and in certain racial groups.
Smoking has one of the strongest and most consistent links to polyp formation. People who smoke one to two packs a day over 20 to 40 years face two to three times the risk of developing adenomas compared to nonsmokers. Even former smokers carry elevated risk, though less than current smokers.
Obesity is another well-established factor. People with a BMI over 30 have roughly double the risk of advanced adenomas compared to those at a healthy weight. The relationship appears to work on a continuum, with higher BMI linked to faster polyp growth, more advanced features, and higher recurrence rates after removal.
Diet plays a role too. Higher intake of animal fat and lower intake of fiber, folate, calcium, and vitamins D and E are all associated with increased risk. Frequent fruit consumption has been linked to lower polyp risk.
Hereditary conditions like familial adenomatous polyposis (FAP) and Lynch syndrome cause polyps to develop at younger ages and in greater numbers. FAP can produce hundreds or even thousands of polyps throughout the colon and rectum. If several close family members have had polyps or colorectal cancer, genetic factors may be involved.
How Rectal Polyps Are Found
Colonoscopy is the primary tool for detecting rectal polyps. A flexible tube with a camera allows the doctor to examine the entire colon and rectum, spot polyps, and remove them during the same procedure. For polyps located specifically in the rectum or lower colon, a flexible sigmoidoscopy can also detect them using a shorter scope. If polyps are found during sigmoidoscopy, a full colonoscopy is typically recommended to check the rest of the colon.
Other screening methods exist, including virtual colonoscopy (which uses CT imaging) and stool tests that check for hidden blood or DNA changes associated with cancer. These can flag potential problems, but if anything abnormal shows up, a colonoscopy is still needed to actually see and remove polyps.
When a polyp is removed or a tissue sample is taken during any of these procedures, you won’t feel it. The tissue goes to a pathologist who examines it under a microscope to determine the type and whether any concerning changes are present.
How Polyps Are Removed
Nearly all rectal polyps can be removed during a colonoscopy without surgery. The technique depends on the polyp’s size and shape.
For the smallest polyps (5 mm or less), cold snare removal is now the preferred approach. A small wire loop snips the polyp off without using any electrical current. This avoids heat-related complications like delayed bleeding or tissue burns and takes less time. Cold snare removal is also used for slightly larger polyps up to about 9 mm.
Larger or pedunculated polyps are typically removed with a hot snare, which uses electrical current to cut through the stalk and seal blood vessels at the same time. This is effective but carries a small risk of delayed bleeding or, rarely, thermal injury to the bowel wall.
For polyps larger than about 20 mm, endoscopic mucosal resection (EMR) lifts the polyp away from the underlying tissue before removing it. Procedure times run about 35 minutes for larger lesions. Complications are uncommon: delayed bleeding occurs in under 1% of cases, and perforation rates range from 0.4% to 1.3%.
How Quickly Polyps Become Dangerous
The progression from a tiny polyp to cancer is slow. A very small (diminutive) adenoma takes an estimated 17 to 48 years to progress through all stages to cancer. A small adenoma takes roughly 8 to 17 years, and a large adenoma takes about 5 to 16 years. These wide ranges reflect different statistical models, but the key point is that the timeline is measured in years to decades, not months.
Size is one of the strongest predictors of risk. Polyps between 6 and 9 mm rarely become malignant. In long-term follow-up studies, none of the patients with small polyps in that range developed cancer, and only 0.4% developed even low-grade precancerous changes. The American Gastroenterological Association has suggested that 3 cm may represent a critical threshold where the risk of a benign polyp becoming malignant rises sharply.
Follow-Up After Removal
Once polyps are removed, follow-up depends on what the pathologist finds. The number of polyps, their size, and their type all determine how soon you need another colonoscopy.
- One or two small adenomas (under 10 mm): Repeat screening in 5 years, sometimes with a stool-based test rather than colonoscopy.
- Three or four small adenomas: Colonoscopy in 5 years.
- Five or more adenomas, any adenoma 10 mm or larger, or adenomas with high-risk features: Colonoscopy in 3 years.
- Multiple sessile serrated lesions: Colonoscopy in 3 years.
After a clean follow-up colonoscopy, the interval between checks typically extends to 5 years. People who had polyps removed are at higher risk for developing new ones, which is why ongoing surveillance matters. Removing polyps before they can progress is one of the most effective ways to prevent colorectal cancer.