Blood in your stool usually comes from somewhere along your digestive tract, and the color of the blood is the single biggest clue to where the problem is. In most cases, the cause is something common and treatable like hemorrhoids or a small tear in the skin around the anus. But because bloody stool can also signal infections, inflammatory diseases, or colorectal cancer, it’s worth understanding what different types of bleeding look like and when they need attention.
What the Color of the Blood Tells You
Bright red blood on the toilet paper or coating the outside of your stool almost always means the bleeding is coming from near the end of the digestive tract: the rectum, anus, or lower colon. The blood hasn’t traveled far, so it still looks fresh.
Dark, maroon-colored blood mixed into the stool points to bleeding higher up in the colon or in the small intestine. The blood has had more time in the digestive tract, so it darkens.
Black, tarry stool with a distinctive sticky texture and foul smell typically signals bleeding in the upper digestive tract, such as the stomach or the first part of the small intestine. Stomach acid breaks down the blood as it passes through, turning it black. That said, bleeding from the right side of the colon or the small bowel can occasionally produce black stool too, so color alone isn’t a perfect map.
The Two Most Common Causes
Hemorrhoids and anal fissures account for the majority of bright red rectal bleeding, especially in adults under 50. They feel different from each other, which helps you tell them apart.
Hemorrhoids cause a dull ache, itching, and sometimes a noticeable lump near the anus. Bleeding can be surprisingly heavy, with blood dripping into the toilet bowl or showing up on toilet paper. External hemorrhoids in particular tend to itch persistently.
Anal fissures, which are small tears in the lining of the anus, cause a sharp, burning pain that can last for hours after a bowel movement. The blood is bright red but typically in smaller amounts than hemorrhoid bleeding. Fissures don’t usually itch. Instead, the sensation is more of a stinging or tearing feeling, especially during a hard or large bowel movement. You won’t feel a lump the way you might with an external hemorrhoid.
A useful rule of thumb: if itching and swelling are your main complaints, hemorrhoids are more likely. If the dominant symptom is sharp pain that feels like a cut, a fissure is the more probable cause.
Infections That Cause Bloody Diarrhea
Bacterial infections in the gut can cause bloody diarrhea, often alongside high fever, cramping, and nausea. The bacteria most commonly responsible include E. coli, Salmonella, Campylobacter, Shigella, and C. diff. These infections typically come from contaminated food, water, or contact with someone who is sick.
Bloody diarrhea paired with a high fever is one of the hallmarks that separates bacterial gastroenteritis from a standard stomach virus. Viral infections cause plenty of diarrhea but rarely produce blood. If your diarrhea is bloody and you’re running a fever, an infection is high on the list of possibilities.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both cause chronic inflammation in the digestive tract and can produce bloody stool. Ulcerative colitis, which affects the colon and rectum, is especially associated with frequent bloody diarrhea, urgency, and cramping. Crohn’s disease can affect any part of the digestive tract and may cause blood in the stool along with abdominal pain, weight loss, and fatigue.
The key difference from a one-time cause like food poisoning is the pattern. Inflammatory bowel disease produces recurring episodes over weeks and months, not a single bad day. If you notice bloody stool coming back repeatedly, especially alongside ongoing cramping or unexplained weight loss, that pattern matters.
Diverticular Bleeding
Diverticular disease, where small pouches form in the colon wall, is common in people over 60. These pouches are usually harmless, but blood vessels running along them can weaken over time and rupture, causing sudden, painless, and sometimes heavy rectal bleeding. The bleeding tends to be maroon or bright red and can be alarming in volume. Importantly, this type of bleeding is distinct from diverticulitis (infection of the pouches). The two conditions develop through different pathways, and bleeding episodes often happen without any infection or inflammation at all. Most diverticular bleeding stops on its own, but heavy or repeated episodes need medical evaluation.
Colorectal Cancer
Blood in the stool is one of the possible signs of colorectal cancer, which is why screening matters even when you feel fine. The U.S. Preventive Services Task Force recommends starting colorectal cancer screening at age 45. From ages 45 to 75, regular screening is recommended for all adults.
Screening options range from a simple stool test you do at home to a full colonoscopy. The fecal immunochemical test (FIT), which detects hidden blood in the stool, has a sensitivity of about 96% for catching colorectal cancer, meaning it correctly identifies the vast majority of cases. A negative result is reassuring, with a negative predictive value of 99.8%. FIT is done annually, while colonoscopy is typically repeated every 10 years if results are normal.
Colorectal cancer doesn’t always cause visible bleeding. It can produce amounts of blood too small to see, which is exactly why screening tests exist. Changes in bowel habits, unexplained weight loss, or a persistent feeling of incomplete emptying are other signs worth paying attention to.
Foods and Medications That Mimic Blood
Before assuming the worst, consider what you’ve eaten or taken recently. Beets and foods with red coloring can make stool look reddish, closely mimicking blood. On the dark end, iron supplements, black licorice, blueberries, activated charcoal, and bismuth-based medications like Pepto-Bismol can all turn stool black in a way that looks alarming but is completely harmless.
The easiest way to rule these out is to stop the suspected food or supplement for a day or two and see if the color returns to normal. True blood in the stool also has other clues: black tarry stool from actual bleeding tends to be sticky and have a noticeably foul smell, unlike the harmless darkening from iron pills.
Signs That Need Immediate Attention
Most causes of bloody stool aren’t emergencies, but some are. Heavy bleeding that doesn’t slow down, lightheadedness or feeling faint, a rapid heartbeat, confusion, or pale and clammy skin all suggest significant blood loss. These are signs your body isn’t keeping up with the bleeding, and they warrant an emergency room visit rather than a scheduled appointment.
Bloody stool combined with severe abdominal pain, especially if it comes on suddenly, also needs prompt evaluation. The same goes for bloody stool in someone who takes blood-thinning medications, since these can turn minor bleeding into something more significant.
For less urgent situations, such as small amounts of bright red blood that you suspect are from hemorrhoids or a fissure, it’s still worth mentioning at your next medical visit, particularly if it’s a new symptom or if it keeps happening. A single episode of minor bright red bleeding after straining is common and usually benign, but recurring blood deserves a closer look.