Anal bleeding is most commonly caused by hemorrhoids or small tears in the skin of the anal canal, both of which are generally harmless and heal on their own. But blood from the rectum can also signal conditions deeper in the digestive tract, so the color, amount, and accompanying symptoms all matter in figuring out what’s going on.
Hemorrhoids: The Most Common Cause
Hemorrhoids are swollen blood vessels in and around the anus. They come in two types, and each bleeds differently.
Internal hemorrhoids sit inside the lower rectum where there are no pain-sensing nerves. When they swell, they can bleed during a bowel movement, producing bright red blood on the stool, on toilet paper, or dripping into the bowl. You typically won’t feel them unless they prolapse, meaning they push through the anal opening. Prolapsed internal hemorrhoids can cause discomfort and a feeling of fullness.
External hemorrhoids form under the skin around the outside of the anus. They’re more likely to itch, ache, or feel tender, especially when sitting. If a blood clot forms inside one (a thrombosed hemorrhoid), the pain can be intense. External hemorrhoids bleed less often than internal ones, but they can bleed if the overlying skin erodes or breaks open.
Straining during bowel movements, sitting on the toilet for long periods, chronic constipation or diarrhea, pregnancy, and heavy lifting all increase pressure on these blood vessels and make hemorrhoids more likely.
Anal Fissures
An anal fissure is a small tear in the thin tissue lining the anal canal. This lining is delicate and highly susceptible to tearing from hard or large stools, straining, or even frequent diarrhea. The hallmark of a fissure is sharp, burning pain during a bowel movement along with minor bleeding that appears as streaks on the stool or toilet paper, not heavy flow.
Fissures can become chronic. When the tear occurs, the ring of muscle around the anus tends to spasm, which restricts blood flow to the area and slows healing. That reduced blood supply is why some fissures reopen repeatedly over weeks or months. Most acute fissures heal within a few weeks with softer stools and proper hygiene, but chronic ones sometimes need additional treatment.
Diverticular Bleeding
Diverticula are small pouches that form along the walls of the colon, particularly in people over 50. Most of the time they cause no symptoms at all. But when a blood vessel near one of these pouches breaks, the bleeding tends to be sudden, painless, and heavy. You may pass a significant amount of dark red or maroon blood. This type of episode usually stops on its own, but even a self-resolving bleed can involve enough blood loss to warrant medical attention.
The key difference from hemorrhoid or fissure bleeding: diverticular bleeding is typically high volume and painless, while hemorrhoid bleeding is low volume and fissure bleeding comes with significant pain.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease cause chronic inflammation in the digestive tract that can damage the intestinal lining and produce rectal bleeding. Unlike hemorrhoid bleeding, this blood is usually mixed in with the stool rather than sitting on top of it, and it comes alongside other symptoms: persistent diarrhea, cramping abdominal pain, urgency, and sometimes weight loss or fatigue. If you’re seeing blood paired with ongoing changes in bowel habits, that combination points away from a simple local cause.
Infections and Radiation Injury
Certain sexually transmitted infections, particularly those affecting the rectum, can inflame the rectal lining (a condition called proctitis) and cause bleeding, discharge, and pain. Bacterial infections from food-borne illness can also irritate the colon enough to produce bloody diarrhea.
People who’ve had radiation therapy to the pelvic area for cancers of the prostate, cervix, or rectum can develop radiation proctitis. The radiation damages the rectal lining, leading to rectal pain, bleeding, and sometimes loss of bowel control. This can appear during treatment or show up months to years later as a chronic condition.
What the Color of the Blood Tells You
The color and consistency of blood in your stool offers a rough map of where the bleeding is coming from. Bright red blood on the surface of stool or on toilet paper generally points to a source near the anus or lower rectum: hemorrhoids, fissures, or rectal inflammation. The closer the source is to the exit, the redder the blood stays.
Dark red or maroon blood mixed into the stool suggests a source higher in the colon, such as diverticular bleeding or inflammatory bowel disease. Black, tarry, sticky stools with a distinctive foul smell indicate bleeding from the upper digestive tract, like the stomach or upper small intestine. Blood that travels through the entire length of the gut gets digested along the way, turning dark. One exception: very rapid bleeding from an upper source can move through fast enough to still appear red when it comes out.
Colorectal Cancer as a Cause
Rectal bleeding can be a symptom of colorectal cancer, though it’s far less common than hemorrhoids or fissures as a cause. Cancerous or precancerous growths (polyps) in the colon or rectum can bleed intermittently, often producing small amounts of blood that may not be visible to the naked eye. When visible, the blood is typically dark red and mixed into the stool. Other signs that raise concern include unexplained weight loss, a persistent change in bowel habits (new constipation or narrower stools), a feeling that the bowel doesn’t empty completely, and fatigue from gradual blood loss.
The U.S. Preventive Services Task Force recommends that adults begin screening for colorectal cancer at age 45, with colonoscopy every 10 years for people at average risk. Screening continues through age 75. If you have a family history of colorectal cancer or other risk factors, your doctor may recommend starting earlier.
Managing Minor Bleeding at Home
If you’re dealing with small amounts of bright red blood and suspect hemorrhoids or a fissure, a few simple steps can help. Increasing fiber and water intake softens stools and reduces straining. Sitz baths, where you soak the anal area in warm water (around 104°F) for 15 to 20 minutes, three to four times a day, can relieve pain and promote healing. Avoid sitting on the toilet longer than necessary, and don’t strain or hold your breath during bowel movements.
Over-the-counter creams and suppositories can reduce swelling and discomfort from hemorrhoids. Most fissures and flare-ups of hemorrhoid bleeding resolve within a few days to a couple of weeks with these measures.
Signs That Need Immediate Attention
Some patterns of rectal bleeding require urgent medical evaluation. Heavy bleeding that doesn’t stop, large clots, or blood that fills the toilet bowl warrants a same-day call or emergency visit. Equally important are systemic signs that suggest significant blood loss: dizziness or lightheadedness when standing up, rapid or shallow breathing, cold or clammy skin, confusion, fainting, blurred vision, nausea, or very low urine output. These symptoms point to a drop in blood volume that needs treatment regardless of the source.
Even without those emergency signs, bleeding that recurs over several weeks, blood mixed into the stool rather than on its surface, or any bleeding accompanied by unexplained weight loss or a new change in bowel habits is worth getting evaluated. A physical exam and, when needed, a colonoscopy can identify or rule out causes that aren’t visible from the outside.