Blood in your stool is common and usually caused by something minor like hemorrhoids or a small tear in the skin around your anus. But it can also signal something more serious, so the color of the blood, the amount, and any symptoms that come with it all matter. Here’s how to make sense of what you’re seeing and when to act on it.
What the Color Tells You
The color of the blood is the single most useful clue about where the bleeding is coming from. Bright red blood typically means the source is low in your digestive tract, usually in your colon, rectum, or anus. The blood is fresh and hasn’t traveled far, so it keeps its red color. You might see it on the toilet paper, coating the stool, or dripping into the bowl.
Dark, tarry, almost black stool points to bleeding higher up, usually in your stomach or upper small intestine. As blood travels through the full length of your digestive system, it gets broken down and oxidized, turning it black and giving the stool a sticky, tar-like texture. This type of bleeding is harder to spot because it doesn’t look obviously like blood, but it has a distinctly foul smell that’s different from normal stool.
The Most Common Causes
Hemorrhoids are the most frequent reason people see blood after a bowel movement. These are swollen blood vessels in and around the rectum that can bleed when you strain, sit for long periods, or pass hard stool. The blood is bright red, usually painless, and often shows up on the toilet paper or the surface of the stool rather than mixed into it. Hemorrhoids don’t always hurt, which is why the blood can catch you off guard.
Anal fissures are the second most common culprit. A fissure is a small tear in the lining of the anus, usually caused by passing a large or hard stool. About 90% of fissures cause pain, compared to hemorrhoids, which are often painless. The pain is sharp, tearing, or burning, hits hardest during a bowel movement, and can linger for minutes to hours afterward. Some people feel it radiating into their thighs or lower back. Like hemorrhoids, the blood is bright red and fresh.
Both conditions share a root cause: straining during bowel movements. Eating more fiber, drinking more water, and avoiding sitting on the toilet longer than necessary can help prevent both.
Less Common but More Serious Causes
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease can both cause blood in stool, but the pattern looks different from hemorrhoids or fissures. With ulcerative colitis, you’ll typically notice bloody diarrhea (sometimes with mucus or pus), along with abdominal cramping, fatigue, fever, weight loss, and an urgent need to go that doesn’t always result in a bowel movement. These symptoms develop over time rather than appearing suddenly, and they tend to come in waves. You may have flare-ups lasting weeks followed by periods of remission where you feel completely fine.
Infections
Bacterial infections from organisms like Campylobacter, E. coli O157:H7, Salmonella, and Shigella can cause acute bloody diarrhea. These are typically picked up from contaminated food or water. A high fever (above about 102°F) suggests Shigella, while E. coli O157:H7 infections usually come without fever. Infectious bloody diarrhea tends to come on fast and hit hard, often with severe cramping.
Colorectal Cancer
This is what most people are really worried about when they search this question. Colorectal cancer can cause blood in the stool, but it’s rarely the only symptom. It usually comes alongside changes in bowel habits that last more than a few weeks, unexplained weight loss, persistent cramping, or a feeling that your bowel doesn’t fully empty. The overall rate of colorectal cancer is about 37.6 per 100,000 people per year. It’s uncommon in younger adults: only about 2% of cases occur in people under 35, and roughly 5% in people 35 to 44. Risk rises meaningfully after 45, which is why screening now starts at that age. The U.S. Preventive Services Task Force recommends routine screening for adults 45 to 75.
Medications
Common anti-inflammatory painkillers like ibuprofen and aspirin can damage the lining of your stomach and intestines over time. These drugs weaken the protective barrier of your digestive tract and reduce blood flow to the gut wall, which can lead to erosions and ulcers that bleed. The bleeding from these upper GI sources often shows up as dark or tarry stool rather than bright red blood. If you take these medications regularly, this is worth knowing about.
Foods and Medications That Mimic Blood
Before you panic, consider what you’ve eaten or taken recently. Several common foods and supplements can make stool look bloody when it isn’t:
- Red stool mimics: beets, red gelatin, red food dyes (including spicy “red hot” snacks), red fruit punch, red licorice
- Black stool mimics: iron supplements, bismuth-based stomach medications (like Pepto-Bismol), activated charcoal, blueberries, large amounts of dark leafy greens like spinach or kale
If you ate beets yesterday and see reddish stool today, that’s almost certainly the explanation. The discoloration from food usually clears within a day or two.
When It’s an Emergency
A small amount of bright red blood on the toilet paper after straining is rarely an emergency. But certain combinations of symptoms mean you need immediate help. Call 911 or get to an emergency room if you’re bleeding from the rectum and also experiencing any of these:
- Dizziness or lightheadedness when you stand up
- Rapid, shallow breathing
- Fainting or confusion
- Cold, clammy, or pale skin
- Blurred vision
- Very low urine output
These are signs of shock, meaning you’ve lost enough blood that your body is struggling to maintain circulation. You should also go to the ER if the bleeding is continuous or heavy, or if it comes with severe abdominal pain or cramping.
What Happens at the Doctor
If you bring up blood in your stool with your doctor, the workup is usually straightforward and starts simple. A digital rectal exam, where the doctor uses a gloved finger to check for hemorrhoids or abnormalities in the rectum, is typically the first step. From there, your doctor may order additional tests depending on your age, symptoms, and what they find:
- Anoscopy or proctoscopy to visually examine your anus and lower rectum
- Fecal occult blood test to detect hidden blood that isn’t visible to the eye
- Flexible sigmoidoscopy to check the lower portion of your colon
- Colonoscopy to examine the entire colon
- Upper endoscopy if dark or tarry stool suggests bleeding from the stomach or upper intestine
Not everyone needs a colonoscopy. A young person with obvious hemorrhoid symptoms may not need any testing beyond a physical exam. Someone over 45 who has never been screened, or anyone with weight loss, changing bowel habits, or a family history of colorectal cancer, is more likely to need a closer look. A stool sample can also help rule out infections or inflammatory conditions like ulcerative colitis by testing for specific markers of inflammation and bacterial pathogens.