Blood in your stool is common and usually not dangerous. Roughly one in seven otherwise healthy adults report experiencing rectal bleeding at some point, and the most frequent cause by far is hemorrhoids. But the color, amount, and accompanying symptoms matter a lot in distinguishing a minor issue from something that needs prompt attention.
What the Color of the Blood Tells You
The shade of blood you see is a useful clue to where the bleeding originates. Bright red blood, whether on the toilet paper, streaked on the surface of your stool, or dripping into the bowl, typically comes from the lower end of your digestive tract: the rectum, anus, or colon. This is the most common presentation and the one most often linked to hemorrhoids or small tears.
Dark red or maroon-colored blood mixed into the stool suggests bleeding higher up in the colon or in the small intestine. Black, tarry, sticky stool with a strong odor points to bleeding above the colon entirely, often in the stomach or upper small intestine. It takes only about half a cup of blood to produce that black appearance, and digestive enzymes transform the blood’s color and consistency as it travels through the gut. If your stool looks like this, the source is likely an ulcer, inflammation, or another issue in the upper digestive tract.
The Most Common Causes
Hemorrhoids are swollen veins in the rectum or anus, and they’re the single most common reason people see blood after a bowel movement. They frequently develop from straining during constipation, sitting for long periods, or during pregnancy. The blood is usually bright red and appears on the tissue or on the surface of the stool. Hemorrhoids can itch or feel uncomfortable, but many cause no pain at all.
Anal fissures, small tears in the lining of the anal canal, are the second most common culprit. They also tend to result from straining or passing hard stools. Unlike hemorrhoids, fissures typically cause a sharp, stinging pain during and after a bowel movement, along with bright red blood on the toilet paper.
Diverticular bleeding happens when small pouches that form in the colon wall (very common after age 40) rupture a blood vessel. This can produce a sudden, painless gush of dark red or maroon blood. It often stops on its own, but because the volume can be significant, it sometimes requires medical evaluation.
Inflammatory bowel diseases like ulcerative colitis and Crohn’s disease cause chronic inflammation in the digestive tract. Bloody diarrhea, abdominal cramping, urgency, and fatigue are hallmarks. The bleeding tends to recur over weeks or months rather than appearing as a one-time event.
Polyps and colorectal cancer can also cause blood in the stool, though they account for a small minority of cases. Polyps are growths on the colon lining that are usually benign but can become cancerous over time. Bleeding from polyps or cancer is often subtle enough that you won’t see it with the naked eye, which is one reason routine screening matters.
Foods and Medications That Mimic Blood
Before you panic, consider what you’ve eaten or taken recently. Beets contain a red pigment called betanin that can turn stool a convincing blood-red color. Large quantities of blueberries can make stool so dark it looks almost black. Black licorice and rainbow-colored candy can do the same.
On the medication side, Pepto-Bismol turns stool jet black, and iron supplements can produce dark green or blackish stool. None of these are harmful, but they can easily be mistaken for bleeding. If you’ve recently consumed any of these, wait a day or two after stopping and see if the color returns to normal.
Signs That Need Immediate Attention
Most rectal bleeding is minor and resolves on its own or with simple treatment. But certain combinations of symptoms signal a more serious situation. Get to an emergency room if rectal bleeding is continuous or heavy, or if it comes with severe abdominal pain or cramping.
Seek emergency help right away if you notice any signs of significant blood loss alongside the bleeding:
- Dizziness or lightheadedness when you stand up
- Rapid, shallow breathing
- Fainting or confusion
- Cold, clammy, or pale skin
- Blurred vision
- Nausea
- Very low urine output
These symptoms suggest your body is losing blood faster than it can compensate, and that requires urgent evaluation.
How the Cause Gets Identified
For occasional, small amounts of bright red blood, a physical exam and a discussion of your symptoms, diet, and bowel habits is often enough for a doctor to identify hemorrhoids or a fissure. A digital rectal exam can confirm swollen tissue or a tear.
When the cause isn’t obvious, or when bleeding is recurrent, dark, or accompanied by other symptoms like weight loss or changes in bowel habits, further testing comes into play. A stool test can detect hidden blood that isn’t visible to the eye. Imaging like a CT scan or ultrasound can reveal structural problems such as diverticular pouches or masses. A colonoscopy, where a camera is guided through the colon, remains the most thorough way to directly visualize the source of bleeding and, when needed, treat it on the spot by removing polyps or cauterizing a bleeding vessel.
Colorectal Cancer Screening
Blood in your stool doesn’t usually mean cancer, but it’s worth knowing where you stand with screening. The U.S. Preventive Services Task Force recommends colorectal cancer screening for all average-risk adults starting at age 45, with regular screening continuing through age 75. “Average risk” means no personal or family history of colorectal cancer, polyps, inflammatory bowel disease, or genetic conditions like Lynch syndrome.
A colonoscopy every 10 years is one of the most effective screening strategies. Less invasive stool-based tests exist and can be done at home, but they’re better at catching cancer that’s already present than at finding precancerous polyps. A stool immunochemical test detects only about 25% of advanced precancerous growths, which is why a colonoscopy remains the gold standard for both detection and prevention.
If you’re under 45 and have no risk factors, a single episode of bright red blood with an obvious explanation like constipation or straining is rarely a reason for a colonoscopy. But persistent or unexplained bleeding at any age warrants a conversation with your doctor about whether earlier screening makes sense for you.