What Causes For Blood In Stool?

Seeing blood in your stool can be alarming, but it is not always a sign of something serious. The most common causes are hemorrhoids, anal fissures, or minor tears from constipation. However, blood in stool can also signal more serious conditions like inflammatory bowel disease, diverticulosis, or colorectal cancer, so you should always have a doctor evaluate it.

What Does the Color of Blood in Stool Tell You?

The color of the blood gives strong clues about where the bleeding is happening in your digestive tract. Bright red blood usually means the bleeding is near the end of your digestive system — the rectum or anus. Dark red or maroon blood often means the bleeding is higher up, in the colon or small intestine.

Black or tarry stool, called melena, means the bleeding is in the upper digestive tract — the stomach or esophagus. The blood has been digested as it traveled through your system, which turns it black. Black stool can also come from iron supplements, bismuth subsalicylate (Pepto-Bismol), or eating dark foods like black licorice.

A simple way to remember: bright red is low, dark red is mid, and black is high. But color alone is not enough to diagnose the cause. You need a medical evaluation to be sure.

What Are the Most Common Causes of Blood in Stool?

Hemorrhoids are the most common cause of bright red blood on toilet paper or in the toilet bowl. These are swollen veins in the rectum or anus that can bleed when you strain during bowel movements. The American Society of Colon and Rectal Surgeons estimates that about 75 percent of adults will have hemorrhoids at some point.

Anal fissures are small tears in the lining of the anus, usually from passing hard or large stools. They cause sharp pain and bright red blood. Fissures are very common in people with chronic constipation.

Diverticulosis is a condition where small pouches form in the lining of the colon. These pouches can bleed, sometimes heavily. About 50 percent of people over age 60 have diverticulosis, according to the National Institute of Diabetes and Digestive and Kidney Diseases.

Colorectal polyps are growths on the inner lining of the colon or rectum. Most polyps are benign, but some can turn into cancer over time. Polyps often bleed slightly, which may only be detected through a fecal occult blood test.

Inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis, causes chronic inflammation in the digestive tract. Bleeding is common, especially with ulcerative colitis, which affects the colon and rectum directly.

Gastritis and peptic ulcers cause bleeding in the stomach or upper small intestine. This usually produces black, tarry stool rather than bright red blood.

When Should You See a Doctor for Blood in Stool?

You should see a doctor any time you notice blood in your stool — even if it is just once. Most causes are not emergencies, but some are. The only way to know is to get checked.

Seek immediate medical care if you also have:

• Large amounts of blood — more than a few teaspoons
• Dizziness, fainting, or feeling lightheaded
• Rapid heart rate or chest pain
• Severe abdominal pain
• Vomiting blood or material that looks like coffee grounds
• Black, tarry stool that is not from medication or food

The American Cancer Society recommends that people at average risk for colorectal cancer start regular screening at age 45. If you are 45 or older and see blood in your stool, do not wait — schedule a colonoscopy. Bleeding can be the first sign of colorectal cancer, and early detection saves lives.

For people under 45 with no other risk factors, a single episode of bright red blood from a known hemorrhoid is less urgent but still worth a phone call to your doctor. If bleeding continues or you have any other symptoms, make an appointment.

How Do Doctors Diagnose the Cause of Blood in Stool?

Doctors start with a medical history and a physical exam. They will ask about the color and amount of blood, your bowel habits, any pain, and your family history of colon problems. A digital rectal exam is common — the doctor inserts a gloved, lubricated finger into the rectum to feel for hemorrhoids, fissures, or masses.

If the cause is not obvious, your doctor will likely recommend a colonoscopy. This is the gold standard test. A thin, flexible tube with a camera goes through your entire colon. The doctor can see the source of bleeding and remove polyps or take tissue samples at the same time. Research published in the New England Journal of Medicine shows that colonoscopy reduces colorectal cancer deaths by about 68 percent.

Other tests your doctor might use include:

• Fecal occult blood test (FOBT) — checks for hidden blood in stool samples
• Flexible sigmoidoscopy — similar to colonoscopy but only examines the lower third of the colon
• CT colonography — a virtual colonoscopy using CT scans
• Upper endoscopy — examines the esophagus, stomach, and upper small intestine if black stool suggests upper GI bleeding

Your doctor will choose tests based on your symptoms, age, and risk factors. Do not assume you need every test — let the doctor guide you.

What Causes For Blood In Stool That Are Less Common but Serious?

Some causes are rare but important to know about. Angiodysplasia is a condition where abnormal blood vessels in the colon bleed. It is more common in older adults and can cause sudden, heavy bleeding. Diagnosis usually requires a colonoscopy.

Ischemic colitis happens when blood flow to the colon is reduced, often from narrowed arteries. It causes abdominal pain and bloody diarrhea. This is more common in people over 60 with heart disease or peripheral artery disease.

Meckel’s diverticulum is a congenital condition where a small pouch forms in the small intestine. It can bleed, especially in children and young adults. This is a rare cause but one that doctors consider when standard tests find nothing.

Colorectal cancer is the most serious cause. The American Cancer Society estimates that about 150,000 new cases of colorectal cancer are diagnosed each year in the United States. Bleeding is often the first symptom. This is why any blood in stool — even a small amount — needs evaluation. Cancer caught early has a 90 percent five-year survival rate. Cancer caught late has a 14 percent survival rate.

Some people report that certain foods like beets, tomatoes, or red food coloring can make stool look red. This is widely claimed though strong evidence is limited to case reports. If you ate beets and your stool is red, think about whether you also have other symptoms. If not, it is probably harmless. But if you are unsure, see a doctor anyway.

Common Misconceptions About Blood in Stool

Misconception: “If the blood is bright red, it cannot be cancer.” This is false. Colorectal cancer can bleed from anywhere in the colon. Bright red blood does not rule out cancer. Only a colonoscopy can tell you for sure.

Misconception: “Blood in stool is always painful.” Not true. Hemorrhoids and fissures often hurt, but polyps, diverticulosis, and early-stage cancer usually do not cause pain. Painless bleeding is common and still needs a workup.

Misconception: “If it stops bleeding, it is fine.” Bleeding that stops does not mean the cause is gone. Polyps and tumors can bleed intermittently. The bleeding may stop for weeks then return. Do not assume you are fine just because the blood disappeared.

Misconception: “You do not need a colonoscopy if you are under 50.” The recommended age for average-risk screening is now 45. If you have symptoms like blood in stool, you may need a colonoscopy at any age. The American Cancer Society updated its guidelines in 2018 based on rising rates of colorectal cancer in younger adults.