Frequent diarrhea is usually caused by something other than cancer, such as an infection, medication, or digestive condition. Colorectal cancer can also change bowel habits, though, so persistent or unexplained symptoms deserve attention. Knowing which warning signs matter can help you decide when to contact a doctor.
Can Frequent Diarrhea Be a Sign of Colorectal Cancer?
Yes, although it is a less common explanation. Colorectal cancer can cause diarrhea, constipation, narrower stools, abdominal pain, rectal bleeding, or a lasting feeling that you still need to go.
These symptoms also occur with noncancerous conditions, so diarrhea alone cannot tell you whether cancer is present. The American Cancer Society lists changes in bowel habits among possible symptoms.
Colorectal cancer may cause no noticeable symptoms in its early stages. The absence of diarrhea or other warning signs does not rule it out.
Frequent Bowel Movements vs. Diarrhea
Going more often than usual is not necessarily diarrhea. NIDDK defines diarrhea as loose, watery stools three or more times a day, or more often than is normal for you.
Tell your doctor how often you go and whether your stools are formed, mushy, or watery. These details can help narrow down the possible causes.
What Research Says About Diarrhea and Cancer
A large study compared 5,075 US adults diagnosed with colorectal cancer before age 50 with 22,378 similar adults who did not have cancer. Researchers examined symptoms recorded in medical records before diagnosis.
Diarrhea had been recorded in 2.8% of the cancer group and 1.4% of the comparison group. Rectal bleeding showed a much stronger association with cancer.
These figures describe how often symptoms were recorded in each group, not the chance that someone with diarrhea has cancer. As an accompanying editorial explains, abdominal pain and diarrhea are common, and most people who experience them do not have colorectal cancer. Persistent or unexplained bowel changes still deserve attention.
Warning Signs That Raise More Concern
A change in bowel habits is more concerning when it persists or comes with other symptoms. Pay attention to the following signs.
A new or lasting change in bowel habits. Diarrhea with no clear cause, symptoms that keep returning, or symptoms that do not improve deserve attention. You do not need to wait a certain number of days before contacting a doctor. NIDDK classifies diarrhea lasting two to four weeks as persistent and diarrhea lasting four weeks or longer as chronic. These terms describe duration, not the likelihood of cancer.
Blood in the stool. Blood may appear bright red, or stool may look dark or black. Hemorrhoids can cause bleeding, but do not assume they are the cause. Rectal bleeding can be a symptom of colorectal cancer. Black, tarry stools may signal bleeding higher in the digestive tract and need prompt medical attention.
Unexplained weight loss, anemia, or fatigue. Losing weight without trying or feeling persistently tired can have many causes, including cancer. Blood tests can identify anemia. Iron-deficiency anemia can develop when ongoing blood loss depletes the body's iron.
Abdominal pain or feeling you still need to go. Cramping or feeling that you need another bowel movement right after going can occur with colorectal cancer, although these symptoms have many other possible causes.
Risk factors for colorectal cancer. Your risk is higher if you have had colorectal polyps or cancer before, have a close family history of colorectal cancer, have inflammatory bowel disease, have received radiation to the abdomen or pelvis, or have an inherited condition such as Lynch syndrome. Colorectal cancer can also affect adults under 50, so being young does not rule it out.
Causes of Frequent Diarrhea
Most diarrhea has causes far more common than cancer. When it starts and whether it follows a particular pattern can help point to the cause.
Diarrhea That Comes on Suddenly
Common causes of sudden diarrhea include viral gastroenteritis, food poisoning, and medication side effects. Recent travel, untreated water, contact with someone who was ill, or a new prescription can provide useful clues.
Antibiotics, magnesium-containing antacids, and some cancer treatments can loosen stools. Tell your doctor about every medication and supplement you take. Do not stop a prescription without talking to them first.
Diarrhea That Follows Certain Foods
Lactose intolerance, dietary fructose intolerance, sucrose intolerance, and sugar alcohols in sugar-free gum and candy can all cause diarrhea. If symptoms repeatedly follow a particular food, note the pattern. It may help your doctor identify a possible intolerance, but it does not confirm one.
Diarrhea That Keeps Coming Back
Up to 5% of people in the United States have chronic diarrhea. Several digestive conditions can cause it.
Irritable bowel syndrome (IBS). IBS can cause recurring abdominal pain and changes in bowel movements, including alternating diarrhea and constipation.
Celiac disease. This immune reaction to gluten can damage the small intestine and interfere with nutrient absorption.
Inflammatory bowel disease (IBD). Crohn's disease and ulcerative colitis cause inflammation in the digestive tract and can lead to diarrhea and bleeding.
Microscopic colitis. This condition causes chronic watery diarrhea. The colon may look normal during a colonoscopy, so diagnosis requires examining a tissue sample under a microscope.
Bile acid diarrhea. This can occur after gallbladder removal or surgery on the lower small intestine. Specific treatments can help.
Changes after abdominal surgery. Operations involving the gallbladder, intestine, pancreas, or stomach can affect digestion and lead to ongoing diarrhea.
Symptoms alone cannot reliably distinguish these conditions. A doctor may recommend tests to identify the cause and guide treatment.
