Blood in your stool is always worth paying attention to, but it’s not always a sign of something dangerous. The most common causes are hemorrhoids and small tears near the anus, both of which are treatable and not life-threatening. That said, rectal bleeding can occasionally signal something more serious, so the color, amount, and accompanying symptoms all matter when figuring out what’s going on.
What the Color of the Blood Tells You
The color of blood in your stool is one of the most useful clues about where the bleeding is coming from. Bright red blood typically originates from the lower part of your digestive tract, usually the colon, rectum, or anus. This is the most common type people notice on toilet paper or in the bowl.
Black, tarry, sticky stools point to bleeding higher up in the digestive system, often the stomach or upper small intestine. Blood turns dark as it travels through the gut and gets partially digested along the way. These stools have a distinctive stickiness and strong odor that’s hard to miss. In rare cases, very rapid bleeding from an upper source like a stomach ulcer can still produce red blood because it moves through the system too quickly to darken.
The Most Common (and Least Serious) Causes
Hemorrhoids and anal fissures account for the majority of rectal bleeding, especially in younger adults. Both produce bright red blood, but they feel quite different.
Hemorrhoids are swollen veins in or around the rectum. They tend to cause itching, a dull ache, and sometimes noticeable bleeding, including larger clots. The discomfort comes and goes. Internal hemorrhoids are painless but can bleed during bowel movements.
Anal fissures are small tears in the lining of the anal canal, usually caused by passing hard stools. They produce a sharp, burning pain that can last for hours after a bowel movement. The bleeding is typically a small amount of bright red blood on the toilet paper. Chronic constipation is the most common trigger for both conditions, because straining and hard stools put pressure on the tissue around the anus.
When It Could Be Something More Serious
Less common but more concerning causes include colon polyps, diverticulosis (small pouches that form in the intestinal wall), inflammatory bowel disease, and colorectal cancer. A British general practice study of 319 patients over age 34 who reported rectal bleeding found that 3.4% were eventually diagnosed with cancer. That means the vast majority had a benign cause, but the risk isn’t zero, particularly for people over 45 or those with a family history.
Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis cause bleeding through chronic inflammation and ulceration of the intestinal lining. These conditions typically come with other symptoms: persistent diarrhea, abdominal pain, unintentional weight loss, and fatigue. The bleeding can range from mild streaks to, in severe cases, significant blood loss that causes dizziness or fainting.
Diverticulosis often causes sudden, painless bleeding that can be heavy but usually stops on its own. Colon polyps, which are small growths on the inner wall of the colon, may bleed intermittently and produce no other symptoms. Some polyps can develop into cancer over time, which is why screening matters.
Medications That Increase Bleeding Risk
Certain medications can cause or worsen gastrointestinal bleeding. Common over-the-counter pain relievers like ibuprofen and naproxen are known culprits. A large meta-analysis found that ibuprofen roughly doubles the risk of GI bleeding, while naproxen increases it about fourfold. These drugs work by reducing inflammation, but they also weaken the protective lining of the stomach and intestines.
The risk climbs higher when pain relievers are combined with blood thinners, corticosteroids, or certain antidepressants (SSRIs). If you’re taking a blood thinner and notice new rectal bleeding, that’s worth bringing up with your doctor promptly. Heavy alcohol use and smoking also contribute to GI bleeding risk.
How Age Changes the Picture
In infants and very young children, the most common causes of bloody stools are anal fissures and allergic reactions to food proteins, particularly cow’s milk protein. These are generally manageable and not dangerous.
In teens and younger adults, hemorrhoids, fissures, and infections account for most cases. Inflammatory bowel disease can also emerge during this period, usually with accompanying symptoms like chronic diarrhea and weight loss.
For adults over 45, the list of possible causes expands to include diverticulosis, polyps, and colorectal cancer. This is why the U.S. Preventive Services Task Force recommends that all adults begin colorectal cancer screening at age 45, with colonoscopy every 10 years being one of the standard options. Adults aged 50 to 75 receive the strongest recommendation for regular screening.
Signs You Need Emergency Care
Most rectal bleeding doesn’t require a trip to the emergency room. But heavy or continuous bleeding paired with certain symptoms means something potentially dangerous is happening. Get emergency help if you experience:
- Dizziness or lightheadedness when standing up
- Fainting or confusion
- Rapid, shallow breathing
- Cold, clammy, or pale skin
- Severe abdominal pain or cramping alongside the bleeding
- Nausea or blurred vision
These symptoms suggest significant blood loss and a drop in blood pressure. Bleeding that won’t stop or that soaks through clothing also warrants immediate attention.
What to Expect at the Doctor
If your bleeding is mild and intermittent, your doctor will likely start with blood tests to check for anemia and assess how well your blood clots. Stool tests can detect hidden blood you might not see with the naked eye.
For a closer look, the most common next step is a colonoscopy, where a flexible camera is guided through the colon to inspect the lining directly. A shorter version of this, called a flexible sigmoidoscopy, examines only the lower portion of the colon and rectum. If these don’t reveal the source, a capsule endoscopy (swallowing a tiny camera in a pill) can image the small intestine as it passes through. In cases of active, heavy bleeding, imaging with contrast dye can pinpoint the exact location of the bleed.
A single episode of a small amount of bright red blood after straining, with no other symptoms, is the most reassuring scenario. Recurrent bleeding, bleeding that happens without an obvious trigger, dark or tarry stools, or bleeding alongside weight loss, fatigue, or changes in bowel habits all justify a closer look sooner rather than later.