When to Worry About Blood in Stool: Warning Signs

Discovering blood in your stool can be alarming, and knowing when to worry about blood in stool versus when it is likely something minor can save you unnecessary anxiety or help you seek timely medical care. Many causes are benign and highly treatable, but certain patterns and accompanying symptoms signal potentially serious conditions that require prompt evaluation. The single most important message of this guide is this: do not assume the bleeding is “just hemorrhoids.” Hemorrhoids are common, but so are several other conditions that look almost identical from the outside, and only a clinician can reliably tell them apart.

Understanding when to worry about blood in stool starts with recognizing what the blood looks like, how much there is, and what other symptoms you are experiencing. This guide walks you through the key warning signs, the full range of common and serious causes, and clear guidance on when to see a doctor and when to treat it as an emergency.

Why You Should Not Assume It Is Just Hemorrhoids

Hemorrhoids and anal fissures are the most common reasons people see bright red blood, and they are usually not dangerous. The problem is that the appearance of the blood alone cannot rule out a more serious cause. Inflammatory bowel disease, colonic polyps, diverticular bleeding, abnormal blood vessels (angiodysplasia), gastrointestinal infections, and colorectal cancer can all produce bleeding that looks similar to a hemorrhoid at first glance. People with known hemorrhoids can also develop a second, unrelated source of bleeding at the same time. For this reason, clinicians treat new or changing rectal bleeding as a symptom to be investigated rather than a diagnosis to be assumed. If you notice blood, the safe approach is to have it evaluated rather than to reassure yourself that you already know the cause.

What Does Blood in Stool Look Like?

Blood in stool can appear in several different ways, and the appearance provides important clues about where the bleeding is coming from:

Bright red blood (hematochezia): Usually indicates bleeding from the lower gastrointestinal tract, including the colon, rectum, or anus. This might appear on toilet paper, in the toilet bowl, or coating the surface of the stool. Common causes include hemorrhoids, anal fissures, and colonic polyps, but brisk bleeding from higher up can also appear bright red.

Dark red or maroon blood: Often suggests bleeding higher up in the colon or from the small intestine. The blood has had some time to partially digest, giving it a darker appearance. This can indicate diverticular bleeding, inflammatory bowel disease, angiodysplasia, or other vascular malformations.

Black, tarry stools (melena): This indicates bleeding from the upper gastrointestinal tract, such as the esophagus, stomach, or duodenum. The blood has been digested, turning it black and giving the stool a tar-like consistency and distinctive foul smell. According to MedlinePlus (NIH), black or tarry stools with a foul smell are a sign of a problem in the upper digestive tract, most commonly peptic ulcers, but also gastritis, esophageal varices, abnormal blood vessels, Mallory-Weiss tears, or cancers of the esophagus, stomach, or duodenum. The National Institute of Diabetes and Digestive and Kidney Diseases notes that upper GI bleeding can be serious and sometimes life-threatening. Melena is a symptom to take seriously and have evaluated promptly.

Occult blood: Blood that is not visible to the naked eye but can be detected through a fecal occult blood test (FOBT) or fecal immunochemical test (FIT). This is why routine screening tests are important for detecting hidden bleeding before it ever becomes visible.

Common Causes That Are Often Less Serious

Many causes of rectal bleeding are benign and highly treatable, though “less serious” does not mean “ignore it.” Hemorrhoids are the most common cause of bright red blood in stool, affecting a large share of adults by age 50. They typically cause painless bleeding during bowel movements and are aggravated by straining, constipation, and prolonged sitting.

Anal fissures, which are small tears in the lining of the anus, cause bright red blood and sharp pain during bowel movements. They are common in people with chronic constipation or hard stools. Dietary factors can also cause stool color changes that mimic blood: beets, red food coloring, cranberries, and tomato products can turn stool red, while iron supplements, bismuth subsalicylate (Pepto-Bismol), and dark foods like black licorice can darken stools. When in doubt, do not assume a color change is dietary – have it checked.

Serious Causes You Should Not Overlook

Because the appearance of blood cannot rule these out, it is worth knowing the range of conditions a clinician will consider. Inflammatory bowel disease (Crohn’s disease and ulcerative colitis) can cause bloody diarrhea, cramping, and urgency. Diverticular disease can cause sudden, sometimes heavy, painless bleeding. Angiodysplasia (fragile, abnormal blood vessels in the bowel wall) is a common cause of bleeding in older adults. Infections and colitis, including certain foodborne infections, can produce bloody stools with fever and diarrhea. Colonic polyps can bleed and are important because some can progress to cancer over time. And colorectal cancer, discussed below, is one of the most important diagnoses to exclude. This is exactly why self-diagnosis is risky – the same symptom can point in very different directions.

Warning Signs That You Should Take Seriously

While many cases of blood in stool are harmless, certain red flags warrant immediate medical attention. You should be concerned if you experience large amounts of blood, either passed during a bowel movement or pooling in the toilet, or bleeding that is continuous. Heavy bleeding can lead to dangerous blood loss and requires urgent evaluation.

Blood accompanied by other symptoms raises the level of concern. Watch for persistent abdominal pain, unexplained weight loss, changes in bowel habits lasting more than a few weeks, fatigue or weakness, fever, or nausea and vomiting. These combinations can indicate conditions like colorectal cancer, inflammatory bowel disease, or serious infections.

Black, tarry stools are particularly concerning because they indicate upper GI bleeding, which can be caused by bleeding ulcers or esophageal varices. This type of bleeding can be life-threatening if not treated promptly. For more information on related conditions, see our guide on symptoms of pancreatic cancer and our medical conditions guide.

Blood in Stool and Colorectal Cancer Risk

One of the most serious potential causes of blood in stool is colorectal cancer, one of the most common cancers in the United States. The American Cancer Society reports that rectal bleeding and blood in the stool are among the most common symptoms, though many early-stage colorectal cancers produce no symptoms at all. That is precisely why bleeding should never be dismissed and why screening matters.

Risk factors that increase concern include being over age 45, having a personal or family history of colorectal polyps or cancer, inflammatory bowel disease, obesity, a diet high in processed meats, smoking, and heavy alcohol use. If you have any of these risk factors and notice blood in your stool, evaluation is especially important – but the absence of risk factors does not make bleeding safe to ignore.

The U.S. Preventive Services Task Force recommends colorectal cancer screening for average-risk adults beginning at age 45 (a Grade B recommendation for ages 45 to 49 and a Grade A recommendation for ages 50 to 75), with screening through age 75 and individualized decisions for ages 76 to 85. People at higher risk may need to start earlier – talk with your clinician. Screening options include colonoscopy, stool-based tests such as FIT and stool DNA tests, and other methods. If you are considering a colonoscopy, our colonoscopy cost guide can help you understand the financial side, and our colon cancer guide covers detection and treatment in more depth.

When to See a Doctor

Schedule an appointment with your doctor if you notice any rectal bleeding that persists for more than a couple of days, even if you suspect hemorrhoids. You should also seek medical evaluation if the bleeding recurs, if you notice a change in your bowel habits, or if you have risk factors for colorectal cancer. In short, any new, persistent, recurrent, or unexplained rectal bleeding deserves a clinician’s assessment. For persistent symptoms from hemorrhoids specifically, our hemorrhoids guide covers management, but a first-time diagnosis should still come from a clinician rather than from self-assessment.

Your doctor will likely perform a physical examination, including a digital rectal exam, and may order blood tests to check for anemia. Depending on the findings, they may refer you for a colonoscopy or other diagnostic imaging to identify the source of bleeding.

Call 911 or go to the emergency room immediately if you experience:

Large-volume, continuous, or uncontrolled rectal bleeding; black or tarry stools; vomiting blood or material that looks like coffee grounds; blood in stool accompanied by dizziness, lightheadedness, or fainting; severe abdominal pain; a rapid heart rate or shortness of breath; or signs of shock (cold clammy skin, confusion, rapid shallow breathing). These symptoms can indicate significant blood loss or a surgical emergency that requires immediate treatment. Do not wait to see whether it resolves on its own.

Diagnostic Tests Your Doctor May Order

To determine the cause of blood in your stool, your doctor may use several diagnostic tools. A colonoscopy is the gold standard for evaluating the colon and rectum, allowing direct visualization and biopsy of any suspicious areas. Upper endoscopy examines the esophagus, stomach, and duodenum when upper GI bleeding is suspected.

Stool tests, including fecal occult blood tests, fecal immunochemical tests, and stool DNA tests, can detect hidden blood and genetic markers associated with colorectal cancer. Blood tests help assess the extent of blood loss and check for anemia, infection, or inflammatory markers. CT angiography or nuclear medicine bleeding scans may be used in cases of active bleeding to locate the source. The right test depends on your symptoms, age, and risk factors, which is another reason evaluation should be guided by a clinician.

Frequently Asked Questions

Is a small amount of blood in stool normal?

Occasional small amounts of bright red blood, especially on toilet paper after wiping, are common and often caused by hemorrhoids or minor anal irritation. However, “common” does not mean it should be ignored indefinitely, and it does not confirm the cause. If it happens repeatedly, changes in pattern, or is new for you, see your doctor for evaluation rather than assuming it is harmless.

Can stress cause blood in stool?

Stress itself does not directly cause rectal bleeding, but it can worsen conditions that do. Stress can aggravate hemorrhoids, contribute to inflammatory bowel disease flares, and play a role in stomach ulcers. Managing stress may help reduce symptoms in these conditions, but new bleeding should still be evaluated.

What does blood in stool look like with colon cancer?

Colon cancer can cause various types of bleeding. Right-sided colon cancers may produce dark red or maroon blood mixed into the stool, while left-sided and rectal cancers more often cause bright red blood. In many cases, the bleeding is occult (hidden) and not visible without testing. Because the appearance is not reliable, screening and evaluation – not self-inspection – are how colorectal cancer is detected.

Should I go to the ER for blood in stool?

Call 911 or go to the emergency room if you are experiencing heavy or continuous bleeding, black tarry stools, vomiting blood, severe abdominal pain, dizziness, fainting, a rapid heart rate, or signs of shock. If the bleeding is small, not accompanied by alarming symptoms, and you feel otherwise well, scheduling an appointment with your doctor within a few days is usually appropriate – but it should still be evaluated.

Can certain medications cause blood in stool?

Yes. Blood thinners (such as warfarin, apixaban, and rivaroxaban), antiplatelet drugs (aspirin, clopidogrel), and NSAIDs (ibuprofen, naproxen) can increase the risk of GI bleeding. If you take these medications and notice blood in your stool, contact your prescribing doctor promptly, and seek emergency care if the bleeding is heavy or you feel unwell. Do not stop a prescribed blood thinner on your own without medical advice.

Take Blood in Stool Seriously

Knowing when to worry about blood in stool comes down to paying attention to the details and resisting the urge to self-diagnose. Bright red spotting from a known hemorrhoid that resolves quickly is usually not an emergency, but even that deserves a clinician’s confirmation the first time. Persistent bleeding, blood mixed into the stool, black tarry stools, or bleeding accompanied by other concerning symptoms all warrant prompt medical evaluation, and the emergency signs above warrant a call to 911. When in doubt, err on the side of caution and contact your doctor. Early detection of serious conditions leads to significantly better outcomes.

Sources

• MedlinePlus (NIH), Bloody or tarry stools – medlineplus.gov
• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Gastrointestinal Bleeding – niddk.nih.gov
• U.S. Preventive Services Task Force, Colorectal Cancer Screening – uspreventiveservicestaskforce.org
• American Cancer Society, Colorectal Cancer Signs and Symptoms – cancer.org
• American College of Gastroenterology (ACG) patient resources – gi.org
• American Society of Colon and Rectal Surgeons (ASCRS), Rectal Bleeding – fascrs.org
• Mayo Clinic, Colonoscopy – mayoclinic.org