Occasional blood in your stool is common but not truly “normal.” About 15% of adults between 20 and 64 experience rectal bleeding in any given year, and the vast majority of cases trace back to something minor like hemorrhoids or a small tear in the anal lining. That said, blood in your stool always has a cause, and some causes need medical attention.
Why Most Cases Are Harmless
The most common reason for blood in your stool, especially if you’re under 40, is anal pathology: hemorrhoids or anal fissures. Both are extremely prevalent, and both result from mechanical stress on delicate tissue rather than from disease.
Hemorrhoids are swollen blood vessels in or around your rectum. They can bleed when you strain during a bowel movement, and you’ll typically notice bright red blood on the toilet paper or in the bowl. They don’t always hurt, which is why they can catch you off guard. Anal fissures are tiny tears in the lining of your anal canal, usually caused by passing hard or large stools. The tissue inside your anus is lined with the same thin, delicate mucosa as the rest of your large intestine, so it tears relatively easily. About 90% of fissures cause sharp pain during or after a bowel movement, which helps distinguish them from hemorrhoids.
Both conditions tend to come and go. You might see blood for a day or two after a bout of constipation, then nothing for weeks. That intermittent pattern is why many people wonder if it’s “normal.” It’s not dangerous in most cases, but it is your body signaling that something is irritating or injuring the tissue.
What the Color of Blood Tells You
The color and appearance of blood in your stool gives a rough indication of where the bleeding originates. Bright red blood generally comes from the lower digestive tract: the colon, rectum, or anus. This is what you’d see with hemorrhoids, fissures, or inflamed tissue in the colon.
Black, tarry stools point to bleeding much higher up, typically in the stomach or esophagus. Blood that travels through the entire digestive tract gets broken down along the way, turning dark and sticky. The most common causes of this type of bleeding are stomach ulcers and inflammation of the esophagus or stomach lining. If your stool looks black and tar-like (not just dark from food), that warrants prompt medical evaluation because upper gastrointestinal bleeding can be significant.
One caveat: certain foods and supplements can mimic blood. Iron supplements, bismuth (the active ingredient in some stomach medications), beets, and dark berries can all change stool color. If you recently ate or took something that could explain it, that’s worth considering before worrying.
Medications That Increase Bleeding Risk
If you take blood thinners, aspirin, or anti-inflammatory painkillers like ibuprofen or naproxen, you’re at elevated risk for gastrointestinal bleeding. These medications can irritate the stomach and intestinal lining directly, and they also make it harder for your body to stop bleeding once it starts. Even low-dose aspirin taken daily for heart health carries a measurable increase in upper gastrointestinal bleeding risk. If you notice blood in your stool while taking any of these, it’s worth mentioning to your doctor even if the bleeding seems minor.
When Blood in Stool Signals Something Serious
While hemorrhoids and fissures explain most cases, blood in your stool can also come from conditions that need treatment. Inflammatory bowel disease, which includes Crohn’s disease and ulcerative colitis, typically appears between ages 20 and 40 and causes bleeding alongside other symptoms like abdominal pain and diarrhea. Diverticular disease, where small pouches form in the colon wall and become inflamed or infected, is the most common cause of significant lower GI bleeding and becomes more likely after age 60.
Colorectal cancer is the concern that brings most people to search this question. The absolute risk is low, particularly for younger adults. Only about 5% of colorectal cancer cases occur in people under 40. But the risk is real and rising in younger populations. A study from the University of Louisville found that among patients under 50 who had colonoscopies, those with rectal bleeding were 8.5 times more likely to be diagnosed with colorectal cancer than those without bleeding. That doesn’t mean rectal bleeding usually indicates cancer. It means bleeding is one of the symptoms that, combined with other factors, can point toward it.
Symptoms That Change the Picture
Isolated, occasional bright red blood with an obvious trigger (hard stool, straining) is the lowest-risk scenario. The picture changes when bleeding appears alongside other symptoms. Watch for:
- Unexplained weight loss without changes to diet or exercise
- Changes in bowel habits lasting more than a few weeks, such as new constipation, diarrhea, or narrower stools
- Anemia symptoms like feeling lightheaded, fatigued, or short of breath
- Abdominal or pelvic pain that persists
- Fever, nausea, or vomiting, especially vomiting blood
- Jaundice (yellowing of the skin or eyes)
Any of these alongside rectal bleeding suggests something beyond a simple hemorrhoid and calls for a medical workup.
How It Gets Evaluated
If you bring rectal bleeding to your doctor, the evaluation typically starts with your medical history, a physical exam, and blood tests to check for anemia and clotting function. A stool test can detect hidden blood you can’t see with the naked eye. From there, the most common next step is a colonoscopy, which lets a doctor visually inspect the entire colon and rectum and, if needed, remove polyps or take tissue samples on the spot.
For adults at average risk with no symptoms, colorectal cancer screening is recommended starting at age 45. But that guideline applies to people with no symptoms. Visible rectal bleeding is a symptom, which means it can justify investigation regardless of your age.
Reducing Bleeding From Everyday Causes
Since constipation and straining are the top triggers for hemorrhoid and fissure bleeding, the most effective prevention is keeping your stools soft and easy to pass. The recommended fiber intake is about 14 grams per 1,000 calories you eat, which works out to roughly 28 grams per day on a standard 2,000-calorie diet. Most people fall well short of that. Good sources include beans, lentils, whole grains, fruits, and vegetables.
Hydration matters too, because fiber works by absorbing water. Without enough fluid, increasing fiber can actually make constipation worse. Beyond diet, avoiding long stretches of sitting on the toilet (scrolling your phone is a common culprit) reduces pressure on rectal blood vessels. When you feel the urge to go, don’t delay it, as waiting can lead to harder stools that are more likely to cause tearing.