Is a Change in Bowel Habits a Sign of Cancer?

Usually not, but a lasting change is worth checking. Diet, stress, and stomach bugs explain most short-term bowel changes. A change that lasts more than a couple of weeks can be a warning sign of colorectal cancer, a cancer of the colon or rectum.

Doctors pay attention to a change from your normal pattern that sticks around. This includes new constipation, new diarrhea, or stools that look narrower than usual. A feeling that your bowel does not fully empty after a movement is another sign worth mentioning. One or two days of an upset stomach after a bad meal is not the pattern doctors mean. Weeks of a new, different bowel pattern is.

A colorectal tumor can physically narrow the passage stool travels through, which changes stool shape and makes it harder to pass. A tumor can also irritate the bowel lining, which speeds up or slows down how your bowel moves. Blood loss from a tumor, even in small amounts you cannot see, can also come with these changes.

Diet changes, new medicines, and stress are common causes of a shift in bowel habits. Irritable bowel syndrome causes ongoing changes in bowel pattern for many people and is not cancer. Infections cause a temporary but sometimes lasting change while your body clears them. Hemorrhoids are a very common cause of bleeding and changes in bowel habits, especially in younger adults.

Your doctor asks exactly what has changed and for how long. They ask whether you have seen blood, and whether you have lost weight without trying. A stool test that checks for hidden blood, called a fecal immunochemical test, is often an early step. A colonoscopy gives the most direct answer: a thin, flexible tube with a camera examines the entire colon, and any abnormal tissue can be removed and checked under a microscope during the same procedure. Ask at the time when the pathology report is expected.

A stool test that shows no blood is reassuring, but some colorectal tumors bleed only occasionally, so a single negative test does not rule out everything. If your bowel habits stay changed after normal results, ask about a colonoscopy directly rather than repeating the stool test alone.

The CDC recommends that most adults start regular colorectal cancer screening at age 45, even with no symptoms at all. Screening can find polyps — small growths that can turn into cancer over time — and remove them before they ever cause a problem. If you are 45 or older and have never been screened, mention that at your visit, whether or not your bowel habits have changed.

• Call your care team the same day if you see blood in the toilet bowl or on the paper. Call too if cramping belly pain has come on with the change.
• Call your care team within a day or two if the new pattern has lasted beyond a couple of weeks. That means diarrhea, constipation, thinner stools, or a bowel that never feels empty. Call too if you have dropped weight without meaning to.

• What has changed [describe], and how long has it lasted?
• Should I have a stool test or go straight to a colonoscopy?
• Am I due for colorectal cancer screening based on my age?
• What symptoms should bring me back sooner?

• National Cancer Institute — Colon Cancer Treatment (PDQ)
• CDC — Screening for Colorectal Cancer