Blood in your stool usually comes from somewhere along your digestive tract, and the color and amount tell you a lot about where it’s coming from and how serious it might be. Most of the time, the cause is something minor like hemorrhoids or a small tear near the anus. But because rectal bleeding can also signal conditions that need treatment, including inflammatory bowel disease or colorectal cancer, it’s worth understanding what different types of bleeding look like and when to act on them.
What the Color of the Blood Tells You
Bright red blood on the toilet paper, in the bowl, or coating the surface of your stool generally comes from the lower part of your digestive tract: the colon, rectum, or anus. This type of bleeding is called hematochezia, and it looks red because the blood hasn’t traveled far or been exposed to digestive enzymes.
Black, tarry, sticky stool is a different signal. This happens when bleeding starts higher up, in the stomach or upper small intestine. As blood moves through the full length of the digestive tract, hemoglobin (the protein that makes blood red) gets broken down by digestive enzymes and turns dark. The result is stool that looks like tar and often has a distinctive foul smell. If you notice this, it typically points to something like a stomach ulcer or irritation in the upper GI tract rather than a problem in the colon.
Maroon-colored stool falls somewhere in between and can come from the middle portions of the digestive tract.
Foods and Supplements That Mimic Blood
Before you panic, consider what you’ve eaten or taken recently. Beets contain a red pigment called betanin that can turn your stool blood-red. It looks alarming, but it’s completely harmless. Iron supplements can make stool dark green or black. Pepto-Bismol turns stool jet black because of the bismuth it contains. Black licorice does the same. Even large amounts of brightly colored candy can mix in your gut and produce dark or unusually colored stool.
If you recently consumed any of these, wait a day or two after stopping and see if the color returns to normal. If it does, the “blood” was never blood at all.
Hemorrhoids and Anal Fissures
These are the two most common causes of bright red blood after a bowel movement, and they behave differently enough that you can often tell them apart. Hemorrhoids are swollen blood vessels inside or around the anus. Internal hemorrhoids typically don’t hurt. You’ll notice bright red blood on the toilet paper or dripping into the bowl, but the bowel movement itself feels normal or only mildly uncomfortable.
Anal fissures, on the other hand, are small tears in the lining of the anus. The hallmark is sharp pain during and sometimes after a bowel movement, along with bright red blood. They’re often caused by passing hard stool or straining. Both conditions can leave behind excess skin near the anus if they persist without treatment. Most cases of either condition improve with increased fiber, adequate water, and avoiding straining, though persistent fissures or hemorrhoids that bleed frequently may need further attention.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease are chronic conditions that cause inflammation in the digestive tract, and they produce different bleeding patterns.
Ulcerative colitis affects only the colon and always starts at the rectum. Its signature symptoms are bloody diarrhea, sudden urgency to use the bathroom, and the frustrating feeling that you still need to go even after you’ve finished. Because the inflammation is concentrated in the lower part of the digestive tract, cramping and bleeding tend to center in the lower abdomen.
Crohn’s disease can affect any part of the digestive tract, though it most commonly involves the small intestine. Diarrhea from Crohn’s is often nonbloody, especially when the small intestine is the main site of inflammation. Instead, the red flags lean more toward belly pain, unintended weight loss, mouth sores, and problems around the anus like painful fissures or fistulas (abnormal tunnels between tissues). Narrowing of the intestines can also cause nausea, vomiting, or bloating. Crohn’s can cause rectal bleeding, but it’s less consistently bloody than ulcerative colitis.
Diverticular Bleeding
Diverticula are small pouches that form in the wall of the colon, most commonly in people over 40. They’re extremely common and usually harmless. Occasionally, though, a blood vessel near one of these pouches ruptures, producing a sudden, painless gush of maroon or bright red blood. Diverticular bleeding is one of the most common causes of significant lower GI bleeding in older adults. It often stops on its own, but the volume of blood can be startling enough to warrant emergency evaluation.
Colorectal Cancer Risk
This is often the fear behind the search, so here are the actual numbers. In a study of patients 45 and older who went to a primary care doctor with a new episode of rectal bleeding, 5.7% turned out to have colorectal cancer or a precancerous growth. That means roughly 94 out of 100 people in that age group had rectal bleeding from something other than cancer.
The risk wasn’t evenly distributed across ages. Among those 45 to 54, about 3.9% had a colorectal growth. The rate dipped slightly for the 55 to 64 group at 1.3%, then rose to 9.5% for those 65 to 74, and 7.9% for those 75 and older. These numbers reinforce that rectal bleeding in middle age and beyond deserves investigation, but they also show that cancer is not the most likely explanation.
Colorectal cancer bleeding tends to be persistent, sometimes subtle enough that you don’t see it with your eyes but enough to cause iron-deficiency anemia over time. Unexplained weight loss, a change in bowel habits lasting more than a few weeks, or a feeling that your bowel doesn’t empty completely are accompanying signs that raise concern.
How Doctors Test for Hidden Blood
Sometimes blood in the stool isn’t visible at all. Screening tests can detect microscopic amounts. The two main types are the guaiac-based test and the fecal immunochemical test (FIT), both done at home with a stool sample. The U.S. Preventive Services Task Force recommends colorectal cancer screening starting at age 45, and an annual FIT is one of the accepted strategies.
FIT is the more accurate option. In studies comparing the two, FIT detected colorectal cancer about 76% of the time versus 39% for the older guaiac test when both were measured against colonoscopy. In larger population-level analyses, FIT’s detection rate climbed to 89% compared to 59% for the guaiac test. Both tests have similar rates of false positives, so FIT catches more real problems without generating significantly more false alarms. A positive result on either test leads to a colonoscopy for a definitive look.
When Rectal Bleeding Is an Emergency
Most rectal bleeding is not an emergency, but certain combinations of symptoms mean you should get to an emergency room or call 911. Heavy or continuous bleeding that doesn’t stop is one clear signal. Severe abdominal pain or cramping alongside bleeding is another.
Signs of shock from blood loss require immediate help. These include rapid, shallow breathing, dizziness or lightheadedness when you stand up, blurred vision, fainting, confusion, nausea, cold or clammy skin, and very low urine output. These signs mean your body is losing blood faster than it can compensate, and waiting it out is not safe.
A small streak of bright red blood on toilet paper after a hard bowel movement, with no other symptoms, is on the opposite end of the spectrum. It’s reasonable to monitor that for a few days, increase your fiber and water intake, and see if it resolves. But if bleeding recurs over several weeks, changes in character, or comes with any of the warning signs above, getting it evaluated gives you a clear answer and, in most cases, reassurance.