Rectal bleeding is surprisingly common. Roughly one in seven adults report experiencing it at some point, and the causes range from minor issues like hemorrhoids to conditions that need prompt treatment. Most of the time, the culprit is something benign and treatable, but the color, amount, and accompanying symptoms all matter in figuring out what’s going on.
Hemorrhoids
Hemorrhoids are the single most common cause of rectal bleeding. They’re swollen veins in or around the anus and rectum, and they tend to bleed during bowel movements. You’ll typically notice bright red blood on the toilet paper, on the surface of the stool, or dripping into the bowl. The bleeding is usually painless with internal hemorrhoids, though external ones can cause a dull ache, itching, and noticeable swelling or a lump near the anus. If itching is your main symptom alongside the bleeding, hemorrhoids are the most likely explanation.
Anal Fissures
An anal fissure is a small tear in the lining of the anal canal, usually caused by passing hard or large stools. The blood is bright red, similar to hemorrhoids, but the sensation is very different. Fissures cause a sharp, burning pain that can last for hours after a bowel movement. Rather than itching, you’ll feel more of a stinging or tearing sensation. A good way to tell the two apart: if the pain is sharp and feels like a cut during or after a bowel movement, a fissure is more likely. If you’re dealing mostly with swelling, itching, and dull discomfort, hemorrhoids are the more probable cause.
What Blood Color Tells You
The color of the blood is a useful clue about where the bleeding originates. Bright red blood typically comes from the rectum, anus, or lower colon. This is what you’d expect with hemorrhoids, fissures, or inflammation in the large intestine. Maroon or dark red blood often points to a source higher up in the colon or small intestine.
Black, tarry stools suggest bleeding from the upper digestive tract, such as the stomach or the first part of the small intestine. Blood that travels that far gets broken down by stomach acid, turning it dark. One important caveat: iron supplements, bismuth (the active ingredient in some stomach medications), and certain foods can also turn stool black without any bleeding. If your stool is black but you’re taking one of these, that’s likely the explanation.
Diverticular Bleeding
Diverticula are small pouches that form in the walls of the colon, most commonly in people over 50. They’re extremely common and usually harmless. But occasionally, a small artery near one of these pouches erodes and bleeds directly into the colon. When this happens, you may pass a noticeable amount of maroon or bright red blood, often without any abdominal pain at all. That painless, sudden quality is the hallmark of diverticular bleeding. Most episodes stop on their own, but they can recur.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both cause inflammation in the digestive tract, and rectal bleeding is a key symptom, particularly with ulcerative colitis. In ulcerative colitis, ulcers form in the lining of the rectum and large intestine, and these ulcers bleed directly into the stool. The blood is usually bright red and often accompanied by diarrhea, urgency, and cramping. You may also notice mucus in your stool during flares.
Crohn’s disease causes bleeding less frequently, but it depends on where the inflammation is located. When Crohn’s affects the colon or rectum, blood in the stool is more likely. Both conditions tend to follow a pattern of flares and remission, so bleeding may come and go over time alongside other symptoms like fatigue, weight loss, and abdominal pain.
Colorectal Polyps and Cancer
Polyps are small growths on the lining of the colon or rectum. Most are harmless, but some can slowly develop into cancer over years. Both polyps and colorectal cancer can cause rectal bleeding, though the bleeding is often so subtle that you won’t see it with the naked eye. When cancer does cause visible bleeding, it may be accompanied by changes in bowel habits, unexplained weight loss, or a feeling that the bowel doesn’t empty completely.
This is the reason screening matters. The U.S. Preventive Services Task Force recommends colorectal cancer screening starting at age 45 for people at average risk. A colonoscopy allows doctors to examine the entire colon and remove polyps before they have a chance to become cancerous. For people who prefer a less invasive option, a fecal immunochemical test (FIT) checks for hidden blood in the stool and can be done at home yearly, though a positive result still requires a follow-up colonoscopy. FIT is better at detecting bleeding from the lower digestive tract than from the stomach, and it can miss some polyps and cancers, making colonoscopy the more thorough option.
Constipation
Chronic constipation is an underappreciated cause of rectal bleeding. Straining to pass hard stools puts pressure on the veins around the anus, which can trigger hemorrhoid bleeding, and hard stool itself can tear the anal lining, creating fissures. In many cases, constipation is the root cause behind what appears to be a hemorrhoid or fissure problem. Addressing it directly often resolves the bleeding.
The recommended daily fiber intake is about 14 grams per 1,000 calories you eat, which works out to roughly 28 grams a day on a standard 2,000-calorie diet. Most people fall well short of that. Increasing fiber gradually through fruits, vegetables, legumes, and whole grains, along with drinking enough water, softens stool and reduces straining. This is the single most effective lifestyle change for preventing the most common causes of rectal bleeding.
When Rectal Bleeding Is an Emergency
Most rectal bleeding doesn’t require a trip to the emergency room, but certain combinations of symptoms signal a serious problem. If you’re experiencing heavy or continuous bleeding alongside any of the following, call 911 or get to an emergency room immediately:
- Dizziness or lightheadedness when you stand up
- Rapid, shallow breathing
- Cold, clammy, or pale skin
- Confusion or fainting
- Nausea with blurred vision
- Very low urine output
These are signs of shock, meaning the body is losing blood faster than it can compensate. Rectal bleeding paired with severe abdominal pain or cramping also warrants immediate medical attention, even without signs of shock. And while a small amount of bright red blood on toilet paper after a hard bowel movement is rarely dangerous, any new or unexplained rectal bleeding that persists for more than a day or two is worth getting evaluated. The cause is usually treatable, and catching the less common causes early makes a significant difference in outcomes.