Blood in Your Stool: What It Could Mean and What to Do Next

What does the color of blood in the stool tell you?

The color and location of blood offer important clues about where the bleeding is coming from 1Ref 1Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI (2021).ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding.Color interpretation of GI bleeding (melena vs. bright red blood) and upper GI bleed sources and management.

Bright red blood on toilet paper or the outside of the stool usually comes from the lower GI tract — the rectum or anus. This is the pattern most often caused by hemorrhoids or small anal fissures (tears).

Bright red blood mixed into the stool can come from the colon.

Dark red or maroon blood mixed throughout the stool often suggests bleeding further up — the colon or small intestine.

Black, tarry, sticky stool (melena) usually means bleeding from the upper GI tract — the stomach or small intestine. This is a more urgent pattern because upper GI bleeds can progress quickly 2Ref 2Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI (2021).ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding.Black tarry stool (melena) as a sign of upper GI bleeding; urgency and risk factors including NSAIDs and liver disease.

Note: certain foods (beets, red food coloring) can make stool appear reddish, and iron supplements or bismuth can make stool very dark. If there is any uncertainty, a clinician can perform a fecal occult blood test.

What are the most common causes?

Hemorrhoids and anal fissures — the most frequent causes of bright red rectal bleeding.

Hemorrhoids are swollen veins in the rectum or around the anus. They are extremely common and typically cause bright red blood on the toilet paper or dripping into the bowl, often without pain — though external hemorrhoids can be very tender. Straining during bowel movements is a major contributing factor 3Ref 3Wald A, Bharucha AE, Limketkai B, Malcolm A, Remes-Troche JM, Whitehead WE, Zutshi M (2021).ACG Clinical Guidelines: Management of Benign Anorectal Disorders.Hemorrhoids and anal fissures as the most common causes of bright red rectal bleeding; clinical features and management.

Anal fissures are small tears around the anus, usually caused by passing a hard or large stool. They typically produce bright red blood alongside sharp pain during and after a bowel movement.

Neither is dangerous in the way other GI bleeding can be, but both should be evaluated if you are not certain of the cause.

Other important causes to know:

*Diverticular bleeding* occurs when small pouches (diverticula) in the colon wall bleed. It is often painless and can produce a significant amount of bright red or maroon-colored blood. It tends to occur in older adults 3Ref 3Wald A, Bharucha AE, Limketkai B, Malcolm A, Remes-Troche JM, Whitehead WE, Zutshi M (2021).ACG Clinical Guidelines: Management of Benign Anorectal Disorders.Hemorrhoids and anal fissures as the most common causes of bright red rectal bleeding; clinical features and management.

*Inflammatory bowel disease (Crohn's disease or ulcerative colitis)* causes inflammation and ulceration of the bowel lining. Blood in the stool is common, often accompanied by diarrhea, cramping, and urgency.

*Colorectal polyps or colorectal cancer* can bleed, sometimes intermittently. Bleeding may be the only early symptom. This is why colorectal cancer screening is recommended starting at age 45 for average-risk adults — earlier with a family history 4Ref 4Shaukat A, Kahi CJ, Burke CA, Rabeneck L, Sauer BG, Rex DK (2021).ACG Clinical Guidelines: Colorectal Cancer Screening 2021.Colonoscopy and other modalities for evaluating rectal bleeding; colorectal cancer screening starting at age 455Ref 5Davidson KW, Barry MJ, Mangione CM, et al. (US Preventive Services Task Force) (2021).Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement.USPSTF recommendation to start colorectal cancer screening at age 45 for average-risk adults; importance of early detection. Colorectal cancer is one of the most preventable cancers when detected early.

*Infectious gastroenteritis* from bacteria such as Salmonella or E. coli can cause bloody diarrhea, usually with cramping and sometimes fever.

*Upper GI bleeds* from stomach ulcers or esophageal varices typically produce black, tarry stool (melena) rather than bright red blood. Use of NSAIDs, aspirin, alcohol, or a history of liver disease increases this risk 2Ref 2Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI (2021).ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding.Black tarry stool (melena) as a sign of upper GI bleeding; urgency and risk factors including NSAIDs and liver disease.

How do age, medications, and history change the picture?

Age over 45: Average-risk adults should be on a colorectal cancer screening schedule. Rectal bleeding is an indication to evaluate sooner if not yet screened 4Ref 4Shaukat A, Kahi CJ, Burke CA, Rabeneck L, Sauer BG, Rex DK (2021).ACG Clinical Guidelines: Colorectal Cancer Screening 2021.Colonoscopy and other modalities for evaluating rectal bleeding; colorectal cancer screening starting at age 455Ref 5Davidson KW, Barry MJ, Mangione CM, et al. (US Preventive Services Task Force) (2021).Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement.USPSTF recommendation to start colorectal cancer screening at age 45 for average-risk adults; importance of early detection.

Family history of colorectal cancer or polyps: Screening should start earlier — often at 40, or 10 years before the youngest affected relative. Blood in the stool needs prompt evaluation regardless of age.

Blood thinners (anticoagulants, antiplatelet drugs): These medications make GI bleeding more likely and can make even minor bleeds more significant. Always tell your clinician you are on them.

NSAIDs or aspirin: Regular use can cause stomach ulcers and increase GI bleeding risk.

Alcohol and liver disease: Cirrhosis can cause esophageal varices that bleed massively — black tarry stool in this context is an emergency.

Inflammatory bowel disease history: Blood in the stool may signal a flare requiring treatment adjustment. IBD also carries a modestly elevated long-term colorectal cancer risk.

What happens when you see a clinician?

Evaluation begins with a history (color, amount, frequency of blood; other symptoms; medications; family history) and a physical exam including a rectal exam. A rectal exam is uncomfortable but brief and extremely informative.

For most patients with bright red rectal bleeding and lower risk, direct visualization of the lower bowel — through anoscopy, flexible sigmoidoscopy, or colonoscopy — is the key diagnostic step 4Ref 4Shaukat A, Kahi CJ, Burke CA, Rabeneck L, Sauer BG, Rex DK (2021).ACG Clinical Guidelines: Colorectal Cancer Screening 2021.Colonoscopy and other modalities for evaluating rectal bleeding; colorectal cancer screening starting at age 45. The choice of test and urgency depends on age, risk factors, and bleeding pattern.

Other tests that may be considered include a complete blood count (to check for anemia from chronic blood loss), upper endoscopy (if melena or upper GI bleed is suspected), fecal occult blood or immunochemical testing, and CT colonography or CT angiography in certain situations.

Do not avoid this conversation out of embarrassment. This is something clinicians discuss every day, and early evaluation makes a meaningful difference — particularly for colorectal cancer, which is highly treatable when found early 5Ref 5Davidson KW, Barry MJ, Mangione CM, et al. (US Preventive Services Task Force) (2021).Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement.USPSTF recommendation to start colorectal cancer screening at age 45 for average-risk adults; importance of early detection.