Bloody Stool: Causes by Color and When to Worry

What the color of blood in stool means

Very fast bleeding from the stomach can also produce red or maroon stool, so a large bleed of any color is an emergency.

Things that mimic blood

Beets, red food dye, cranberries and tomato skins can turn stool red. Iron tablets, bismuth subsalicylate (in some stomach remedies), blueberries and black licorice can turn it black, but this stool is not sticky and tarry. If in doubt, a simple stool test can check for blood.

Common causes

Hemorrhoids

Swollen veins in the anal canal are the commonest cause of bright red bleeding. The blood is on the paper or drips into the bowl after a bowel movement, usually painlessly. Itching and a soft lump at the anus are common. See hemorrhoids.

Anal fissure

A small tear in the lining of the anus, usually from passing a hard stool. It causes sharp pain during and after bowel movements, often lasting an hour or more, with a little bright red blood. See anal fissure.

Infections

Bacteria such as Campylobacter, Salmonella, Shigella and toxin-producing E. coli, and C. difficile after antibiotics, can cause bloody diarrhea with cramps and fever. Some E. coli infections can lead to kidney failure in children, so bloody diarrhea in a child needs prompt care.

Serious causes

• Colorectal polyps and cancer: often cause no symptoms, or only small amounts of blood mixed into the stool, a change in bowel habit, iron deficiency anemia or weight loss. Colorectal cancer is increasingly diagnosed in adults under 50. See colorectal cancer.
• Inflammatory bowel disease: ulcerative colitis causes bloody diarrhea with urgency and mucus. Crohn's disease causes pain, diarrhea and weight loss, sometimes with bleeding.
• Diverticular bleeding: sudden, painless, sometimes heavy red or maroon bleeding in older adults. See diverticular disease.
• Peptic ulcers: bleeding stomach or duodenal ulcers cause black stool, often in people taking NSAIDs or aspirin, or with H. pylori infection. See peptic ulcer.
• Ischemic colitis: reduced blood flow to the colon causes sudden cramping left-sided pain followed by bloody diarrhea, mainly in older adults.
• Angiodysplasia: fragile blood vessels in the gut lining, common in older adults and people with kidney disease.
• Radiation proctitis after pelvic radiotherapy.
• Esophageal varices in liver cirrhosis, which cause vomiting of blood and black stool.

Symptoms that come with it and what they suggest

• Pain on passing stool: fissure.
• Itching and a lump: hemorrhoids.
• Diarrhea, urgency, mucus: colitis or infection.
• Weight loss, tiredness, change in bowel habit: cancer or inflammatory bowel disease.
• Upper abdominal pain, indigestion, NSAID use: ulcer.
• Dizziness, breathlessness, paleness: significant blood loss or anemia.

How doctors find the cause

A doctor will ask about the color and amount of blood, how often it happens, bowel habits, pain, weight, medicines (especially blood thinners, aspirin and NSAIDs), and family history. They will examine the abdomen and do a rectal examination, sometimes with a short scope (proctoscopy) to see hemorrhoids or a fissure.

Tests may include:

• a full blood count to check for anemia, and iron studies
• a fecal immunochemical test (FIT) for hidden blood in some settings
• colonoscopy to examine the whole colon and remove polyps
• upper endoscopy for black stool
• CT angiography or capsule endoscopy for hard-to-find bleeding

Many guidelines recommend colonoscopy for anyone over 45 with rectal bleeding, because hemorrhoids are common and can coexist with a more serious cause.

Treatment and home care

Treatment depends on the cause:

• Hemorrhoids and fissures: a high-fiber diet, 25 to 35 g a day, plenty of fluids, stool softeners, avoiding straining, warm sitz baths, and creams. Fissures may need prescription ointments that relax the anal muscle.
• Infection: fluids, and sometimes antibiotics.
• Inflammatory bowel disease: anti-inflammatory and immune-modifying medicines.
• Polyps: removal during colonoscopy.
• Ulcers: acid-suppressing medicines and treatment of H. pylori.
• Major bleeding: hospital care with fluids, transfusion and endoscopic or radiological treatment to stop the bleeding.

Do not stop prescribed blood thinners without talking to your doctor.

Prevention

• Eat enough fiber and drink water to keep stools soft.
• Do not strain or sit on the toilet for long periods.
• Get screened for colorectal cancer from age 45, or earlier if you have a family history.
• Limit NSAID use, and take them with food if needed.

Frequently asked questions

Is bright red blood in stool serious?

Usually it comes from hemorrhoids or an anal fissure, which are not dangerous. But polyps, cancer and colitis can also cause bright red bleeding. See a doctor if you are 45 or over, if bleeding keeps happening, or if you have a change in bowel habit, weight loss or tiredness.

What does dark red or black blood in stool mean?

Dark red or maroon blood usually comes from the colon or small intestine. Black, tarry stool usually means bleeding from the stomach or duodenum, such as from an ulcer. Both need prompt medical assessment, and urgently if you feel dizzy or faint.

Can stress cause blood in stool?

Stress does not directly cause bleeding, but it can worsen conditions that bleed, such as inflammatory bowel disease, and lead to constipation and straining that aggravate hemorrhoids or fissures. Blood in the stool should always have its cause checked rather than being put down to stress.

Should I go to the ER for blood in my stool?

Go to the ER for heavy bleeding, clots, black tarry stool, or bleeding with dizziness, fainting, a rapid heartbeat or severe abdominal pain. For a small amount of bright red blood without other symptoms, a prompt appointment with your primary care doctor is usually appropriate.

What foods can make stool look bloody?

Beets, red gelatin or drinks with red dye, cranberries and tomato skins can make stool look red. Iron supplements, bismuth stomach remedies, blueberries and black licorice can make it look black. If you are unsure, a doctor can test the stool for blood.