Rectal bleeding is extremely common, showing up in roughly 13% to 34% of the general population at some point. The vast majority of cases, over 96%, turn out to be non-cancerous. Hemorrhoids are the single most frequent cause, but several other conditions can produce blood in or on your stool, and the color and pattern of the bleeding often point toward the source.
What the Blood Looks Like Matters
The color of the blood you see gives a rough indication of where in your digestive tract it’s coming from. Bright red blood on the toilet paper or dripping into the bowl typically originates near the anus or lower rectum, from conditions like hemorrhoids or fissures. Darker red or maroon-colored blood mixed into the stool suggests a source higher up in the colon, such as diverticular bleeding or polyps. Black, tarry stools (called melena) usually signal bleeding from the stomach or upper intestine, where blood has been partially digested on its way through.
These patterns aren’t absolute. A very fast bleed from the upper digestive tract can still produce red blood, and a slow bleed from the colon can darken by the time it passes. But as a general guide, brighter blood means a source closer to the exit.
Hemorrhoids
Hemorrhoids are swollen veins inside the rectum or under the skin around the anus, similar to varicose veins in the legs. They’re the most common cause of rectal bleeding in middle-aged and older adults. Internal hemorrhoids sit inside the rectum and typically cause painless, bright red bleeding you notice on the toilet paper or in the bowl. External hemorrhoids form under the skin around the anus and tend to produce a dull ache, pressure, or continuous throbbing that can last throughout the day. If a blood clot forms inside an external hemorrhoid (a thrombosed hemorrhoid), the pain can be sudden and severe.
Straining during bowel movements, sitting for long periods, pregnancy, and chronic constipation all increase your risk. Most hemorrhoids improve with increased fiber intake, proper hydration, and avoiding prolonged straining. They can recur, but they’re rarely dangerous.
Anal Fissures
An anal fissure is a small tear in the thin lining of the anus. It commonly happens after passing a hard stool during constipation or after childbirth. Fissures cause blood-streaked stools and a sharp, searing pain during bowel movements that patients often describe as feeling like passing shards of glass. After the bowel movement, a deep ache can linger for minutes to hours.
You can sometimes see a visible crack in the skin around the anal opening. In chronic cases, a small skin tag may form near the tear. Fissures are easily confused with hemorrhoids since both relate to constipation and both cause bleeding, but the pain pattern is distinct: hemorrhoids produce a duller discomfort, while fissures cause that intense, tearing sensation tied specifically to passing stool.
Colon Polyps
Polyps are growths that protrude from the inner wall of the colon, sometimes described as mushroom-shaped. They’re common, and most are harmless. Larger polyps can bleed, producing blood mixed into the stool rather than sitting on its surface. You may not notice any symptoms at all until a polyp is found during a routine screening.
The reason polyps matter is that some types can slowly transform into colorectal cancer over years. This is why screening is recommended starting at age 45 for most people, with a colonoscopy every 10 years for those at average risk. Catching and removing polyps early eliminates the cancer risk from those growths entirely.
Diverticular Bleeding
Diverticulosis means small pouches have formed in weak spots along the colon wall. This is extremely common with age, and most people with diverticulosis never have problems. But in 3% to 5% of cases, one of those pouches bleeds. The bleeding is arterial, caused by repeated mechanical or chemical irritation inside the pouch that gradually thins the lining and injures small blood vessels running through the colon wall.
Diverticular bleeding typically shows up as a sudden, painless, large-volume bleed. You may pass a significant amount of dark red or maroon blood with little warning. It can be alarming, but the bleeding stops on its own in most cases. It does tend to recur, though, and repeated episodes sometimes require further intervention.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease are chronic conditions where the immune system attacks the lining of the digestive tract. In ulcerative colitis, inflammation and ulcers form along the inner surface of the colon and rectum. The bleeding pattern depends on how much of the colon is involved.
When only the rectum is inflamed (ulcerative proctitis), rectal bleeding or urgency to use the bathroom may be the only symptom. As inflammation extends further into the colon, you’re more likely to experience bloody diarrhea, abdominal cramps, fatigue, and weight loss. The diarrhea often contains mucus or pus along with blood. The underlying cause isn’t fully understood, but it appears to involve a combination of genetic susceptibility, an overactive immune response, and imbalances in the natural gut bacteria.
Unlike hemorrhoids or fissures, inflammatory bowel disease doesn’t resolve on its own and requires ongoing management to control flare-ups and prevent long-term damage to the colon.
Angiodysplasia
In adults over 60, fragile clusters of abnormal blood vessels can develop along the wall of the colon. This condition, called angiodysplasia, is the most common vascular abnormality in the digestive tract and the leading cause of hard-to-explain GI bleeding in older patients. These abnormal vessels are most often found in the cecum (the beginning of the large intestine) and the rectosigmoid area.
Risk factors include advanced age, diabetes, high cholesterol, valvular heart disease, and use of blood thinners. The bleeding is often intermittent and can range from mild to significant. Because the abnormal vessels are small and flat, they can be difficult to detect and may require specialized imaging during a colonoscopy.
Infections
Certain bacterial, viral, and parasitic infections can inflame the colon or rectum enough to cause bleeding. Foodborne pathogens like Salmonella, Shigella, and certain strains of E. coli are well-known culprits. Sexually transmitted infections affecting the rectum, including gonorrhea, chlamydia, and herpes, can also produce rectal bleeding alongside pain and discharge. Infectious causes typically come with other symptoms like diarrhea, fever, and cramping, and they usually resolve once the infection is treated.
Colorectal Cancer
Cancer accounts for only about 3.4% of rectal bleeding cases, but it’s the cause that needs to be ruled out, especially in older adults. Bleeding from colorectal cancer can look like any of the patterns described above, from bright red blood to darker blood mixed into the stool, which is part of what makes it tricky to distinguish from benign causes based on appearance alone.
Warning signs that raise concern beyond the bleeding itself include unexplained weight loss, a change in bowel habits lasting more than a few weeks (new constipation, narrower stools, or persistent diarrhea), a feeling that the bowel doesn’t empty completely, and fatigue from slow, chronic blood loss you may not even see. The current recommendation from the U.S. Preventive Services Task Force is that adults between 45 and 75 be screened for colorectal cancer, regardless of whether they have symptoms.
When Rectal Bleeding Is an Emergency
Most rectal bleeding is not an emergency. A small amount of bright red blood after a hard bowel movement, especially if you have known hemorrhoids, usually doesn’t require urgent care. But certain patterns signal a more serious situation. Heavy bleeding that doesn’t stop, blood clots in your stool, feeling dizzy or lightheaded while bleeding, and a rapid heartbeat are all signs of significant blood loss. If the bleeding is accompanied by severe abdominal pain, fever, or confusion, that also warrants immediate medical attention.
Even mild rectal bleeding that persists for more than a week or two, or that keeps coming back, is worth getting evaluated. A physical exam and, if needed, a closer look at the colon through a scope can usually identify the cause quickly and rule out anything serious.