Rectal bleeding has many possible causes, and most of them are not serious. Hemorrhoids are the single most common reason, but the list ranges from minor tears in the skin to infections, inflammatory conditions, and occasionally cancer. About 1 in 7 otherwise healthy adults report a history of rectal bleeding, and only a small fraction visit a doctor about it. Understanding what different types of bleeding look like can help you figure out what’s likely going on and whether you need prompt attention.
What the Color of Blood Tells You
The color of the blood you see is one of the most useful clues about where the bleeding is coming from. Bright red blood on toilet paper or in the bowl typically means the source is near the end of the digestive tract: the rectum or anus. This is the most common presentation and often points to hemorrhoids or a small tear.
Maroon or dark red blood mixed into the stool suggests bleeding higher up in the colon, which can happen with diverticular disease, inflammatory bowel disease, or certain infections. Black, tarry stool is a sign that blood has been digested on its way through the gut, meaning the source is likely in the stomach or upper small intestine. Peptic ulcers are a classic cause of this darker presentation.
Hemorrhoids
Swollen veins in the rectum or anus are by far the most frequent cause of rectal bleeding. They develop when pressure builds up in that area, usually from straining during bowel movements, sitting for long periods, pregnancy, or chronic constipation. Internal hemorrhoids tend to bleed painlessly. You might notice bright red streaks on toilet paper or dripping into the bowl after a bowel movement. External hemorrhoids, which form under the skin around the anus, are more likely to cause pain, itching, and swelling alongside any bleeding.
Most hemorrhoids improve on their own within a few days to a couple of weeks, especially with added fiber, more water, and less straining. Persistent or recurring hemorrhoids sometimes need treatment to shrink or remove them.
Anal Fissures
An anal fissure is a small tear in the lining of the anal canal. It shares many of the same triggers as hemorrhoids, particularly straining to pass hard stool. The hallmark difference is pain: fissures cause a sharp, stinging sensation during a bowel movement, sometimes followed by burning or itching that lingers afterward. The blood is fresh and red, often visible on the stool or on toilet paper.
Because the symptoms overlap so much with hemorrhoids, it’s common to confuse the two. Fissures usually heal within a few weeks if the stool stays soft and you avoid straining. Chronic fissures that don’t respond to these changes may need additional treatment.
Diverticular Bleeding
Diverticulosis, the formation of small pouches in the wall of the colon, is extremely common as people age. Most of the time these pouches cause no symptoms at all. But when a blood vessel inside one of these pouches is injured, it can bleed, sometimes heavily. Diverticular bleeding tends to come on suddenly and intensely, producing a significant amount of maroon or bright red blood in a short period.
The good news is that this type of bleeding usually stops on its own. The bad news is that even a self-limiting episode can involve enough blood loss to require medical evaluation. If you suddenly pass a large volume of blood, that warrants prompt attention regardless of the suspected cause.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both involve chronic inflammation of the digestive tract, and both can cause rectal bleeding. Ulcerative colitis primarily affects the large intestine and rectum, so bloody diarrhea is one of its defining symptoms. Crohn’s disease more often involves the small intestine but can affect any part of the gut. When it does cause bleeding, deep ulcers in the intestinal wall can erode into blood vessels. Bleeding from Crohn’s disease tends to originate in the left side of the colon, partly because formed stool in that area rubs against inflamed tissue.
Both conditions come with additional symptoms that set them apart from a simple hemorrhoid: persistent diarrhea, abdominal cramping, fatigue, unintentional weight loss, and episodes that flare and subside over months or years. These are chronic conditions that require ongoing management.
Infections
Certain bacterial infections in the colon can cause bloody diarrhea. Common culprits include E. coli and C. difficile (an infection that often develops after antibiotic use). The pattern is distinct: sudden onset of frequent, watery, bloody stools along with cramping and sometimes fever. Most people can identify a clear trigger, such as contaminated food or recent hospitalization.
Infectious colitis usually resolves with appropriate treatment, though some infections like C. difficile can be stubborn and recur.
Ischemic Colitis
When blood flow to part of the colon is temporarily reduced, the tissue doesn’t get enough oxygen and becomes damaged and swollen. This is called ischemic colitis, and it causes bright red or maroon blood in the stool, often accompanied by abdominal cramping. It’s more common in older adults and in people with conditions that affect blood circulation. The bleeding can occur with or without a bowel movement.
Colon Polyps and Colorectal Cancer
Polyps are small growths on the inner lining of the colon. Most are harmless, but some can develop into cancer over time. Both polyps and colorectal cancer can bleed when stool passes over them and irritates or damages the abnormal tissue. This bleeding is often subtle, sometimes too small to see with the naked eye, which is why screening tests that detect hidden blood in the stool are so important.
The U.S. Preventive Services Task Force recommends that all adults begin colorectal cancer screening at age 45 and continue through age 75. People with inflammatory bowel disease, a family history of colorectal cancer or polyps, or certain genetic syndromes may need to start earlier. Between ages 76 and 85, the decision depends on individual health and prior screening history.
Rectal bleeding alone doesn’t mean cancer. But bleeding that persists, changes in bowel habits that last more than a few weeks, unexplained weight loss, or a feeling that the bowel doesn’t empty completely are all reasons to get evaluated.
Medications That Cause Bleeding
Blood thinners, anti-clotting medications, and drugs that irritate the digestive tract (like certain anti-inflammatory painkillers) can all cause or worsen rectal bleeding. Sometimes the medication doesn’t cause the bleeding directly but makes an existing source bleed more than it otherwise would. If you’re on any of these medications and notice blood in your stool, that’s worth bringing up with whoever prescribes them.
How Rectal Bleeding Is Evaluated
When you report rectal bleeding, the workup typically starts with blood tests and sometimes a stool sample to check for hidden blood or signs of infection. From there, the approach depends on what’s suspected. An anoscopy uses a small tube to look directly at the anus and is the quickest way to spot hemorrhoids or fissures. A sigmoidoscopy examines the rectum and the lower portion of the colon using a flexible lighted tube. A colonoscopy covers the entire colon and rectum. You’re sedated for a colonoscopy, so you sleep through it, and it allows the doctor to both find and sometimes treat the source of bleeding in the same procedure.
Signs That Need Immediate Attention
Most rectal bleeding is minor and resolves without emergency care. But heavy or continuous bleeding, especially with severe abdominal pain or cramping, calls for an emergency room visit. Significant blood loss can lead to shock, which shows up as rapid shallow breathing, dizziness or lightheadedness when standing, blurred vision, confusion, cold or clammy skin, and fainting. If any of those symptoms accompany rectal bleeding, that’s a 911 situation.
Even when the bleeding is small and painless, recurrent episodes deserve investigation. A single bright red streak on toilet paper after a hard bowel movement is almost always a hemorrhoid or fissure. But bleeding that keeps coming back, changes color, or arrives alongside other new symptoms is your body signaling that something deeper is going on.