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What Causes Bloody Diarrhea?

Any blood in the stool may signal a more serious problem.
Pieces of stools with blood and mucus
Written by Shria Kumar, MD.
Therapeutic Endoscopy Fellow, MD Anderson Cancer Center, Houston, TX
Medically reviewed by
Last updated April 8, 2024

Bloody diarrhea quiz

Take a quiz to find out what's causing your bloody diarrhea.

6 most common cause(s)

Crohn's Disease
Illustration of various health care options.
Colonic neoplasm
Food Poisoning
Illustration of a health care worker swabbing an individual.
Intestinal ischemia
Illustration of a doctor beside a bedridden patient.
Parasite infections

Bloody diarrhea quiz

Take a quiz to find out what's causing your bloody diarrhea.

Take bloody diarrhea quiz

What is bloody diarrhea?

Spotting blood in the toilet or on the toilet paper can be upsetting. And blood is always cause for concern. That said, a trace of blood in your stool (whether well-formed or diarrhea-like) can be caused by a relatively minor condition, such as mild constipation or hemorrhoids.

But if you’re noticing more than a trace, or if the blood is accompanied by other stomach issues, you may need to see a doctor. Possible culprits include a bacterial or parasite infection, inflammatory bowel diseases (such as Crohn’s disease or colitis), and colorectal cancer.

1. Bacterial infection


A stomach bug can be caused by bacteria. Common bacterial infections that can cause bloody diarrhea include E. coli, Campylobacter, Salmonella, Shigella, and Clostridium difficile infection (C. diff).

Bacterial infections may be contagious and can spread if an infected person does not wash their hands thoroughly.

E. coli, Campylobacter, Salmonella, and Shigella all come from contaminated foods or water, and are often due to improper handling or cooking. C. difficile often occurs in people taking antibiotics for other infections. It’s highly contagious and is often passed from patient to patient in the hospital. People who are hospitalized or recently discharged are at high risk.

Bacterial infections can sometimes be serious and spread through the body, so early diagnosis and treatment is important. You may be given antibiotics.

2. Hemorrhoids

Pro Tip

Bloody diarrhea doesn’t necessarily indicate an emergency! —Dr. Shria Kumar


  • Blood on toilet paper

A hemorrhoid occurs when the small blood vessels around your anus become swollen and inflamed. They can be internal (inside the rectum) or external (outside). Hemorrhoids themselves may cause pain with bowel movements or blood on the toilet paper.

If you have diarrhea, this can irritate your hemorrhoids and cause some bleeding. Your doctor may recommend ointments or stool softeners (if you are constipated) to help reduce trauma to the hemorrhoids.

3. Inflammatory bowel disease


Inflammatory bowel disease (IBD) is inflammation of the bowel. There are two types: Crohn’s disease and ulcerative colitis. It is due to multiple factors, including genetics, the environment, and your body’s immune system. Symptoms may develop gradually or occur suddenly.

Untreated IBD causes inflammation throughout the digestive tract, which can lead to malnutrition, cancers, bleeding, and overall poor health.

Managing the condition involves eliminating the inflammation with medication and diet. Treatment includes taking anti-inflammatory medications, such as topical or oral steroids, and immunologic medications that tamp down your immune system. In some cases, surgery may be needed.

Once diagnosed with IBD, you will require regular check ups with your gastroenterologist (digestive disease doctor). You may be at increased risk of colorectal cancer, so you will need more regular cancer screenings, such as colonoscopies.

4. Intestinal ischemia


  • Sudden nausea and vomiting
  • Sudden bloody diarrhea
  • Sudden, severe abdominal pain

Ischemia occurs when blood flow is low. This happens when there is a blockage in one of the arteries in the abdomen that supplies your intestines with blood. This blockage could be plaque or a blood clot. The loss of blood flow can damage your intestines. Ischemia is a life-threatening medical emergency.

People with very high or low blood pressure and heart disease may be at risk. Using certain illegal drugs like cocaine and methamphetamine may also cause ischemia.

If you have a clot, it is treated with "clot-busting" drugs. If there’s a blockage, you may need emergency surgery to remove the blockage as well as the damaged part of the intestine.

5. Colorectal cancer

Dr. Rx

Establishing a story around the bloody diarrhea helps me a lot. When did these symptoms start? Are they accompanied by other symptoms (even non-bowel related symptoms)? Did the patient travel anywhere or eat somewhere and now other people are sick, too? What’s their overall health profile? Are they in severe pain, are they bleeding profusely (things that would prompt me to admit them to a hospital, get bloodwork and imaging studies). —Dr. Kumar


  • Weight loss
  • Change in appetite
  • Change in bowel habits, often including blood

Cancer of the colon (large intestine) or rectum is considered colorectal cancer. Colorectal cancer typically affects adults over age 50, but it can happen in younger adults.

The cancers usually begin as small polyps that become cancerous over time. This is why a colonoscopy screening test, which detects and removes these small polyps before they become cancerous, is important. If you are between age 50 and 75, the Centers for Disease Control and Prevention (CDC) recommends colorectal cancer screening. People at increased risk may be advised to start screening even earlier.

Colorectal cancer usually causes some changes to your bowel habits and eating patterns. Treatments include surgery, chemotherapy, and/or radiation.

6. Parasite infections


  • Diarrhea that may be bloody
  • Fever
  • Vomiting
  • Stomach cramps
  • Fatigue or weakness
  • Weight loss

You can pick up a parasite infection by consuming food or water containing parasites like hookworm or amoebiasis. Or if your hands come in contact with a parasite and you touch your face.

While parasite infections are more common in underdeveloped parts of the world where drinking water is contaminated, you can catch it in the U.S.

Blood and stool tests can determine the type of parasite, according to the CDC. Your doctor will prescribe an anti-parasitic medication.

Other possible causes of bloody diarrhea

Other less common causes of bloody diarrhea include:

  • Viral infections
  • Vascular inflammation (vasculitis), such as hemolytic uremic syndrome
  • Bowel obstruction
  • Intussusception
  • Diverticulosis

When to call the doctor

Pro Tip

Important questions to ask your doctor: What caused this? Do I need any treatment for this? —Dr. Kumar

Because bloody diarrhea is not normal, you should call your doctor if you see more than a few streaks of blood in your stool. Always seek medical care if you also feel lightheaded, can’t eat or drink, or have severe abdominal pain.

As bloody diarrhea can be caused by parasites or bacteria, be sure to let your doctor know about any recent trips. They will want to rule out parasites or bacteria that may be common in the places where you traveled.

In addition, the more information you share about your diet, recent medications, and lifestyle, the better your doctor can assess your symptoms. In some cases, medications could be causing your stool to appear bloody.

You should also call the doctor if you have more than one episode of bloody diarrhea, or the diarrhea is accompanied by:

  • Abdominal pain
  • Nausea or vomiting
  • Fever
  • Dizziness
  • Confusion
  • Shortness of breath
  • Chest pain
  • Headache
  • Fatigue

Should I go to the emergency room for bloody diarrhea?

You should go to the ER if you have any of these signs, which can indicate a serious problem.

  • Blood looks clumpy like coffee grounds or is dark and tarry.
  • Blood seems to be filling the toilet or does not stop when you stand up.
  • You’re experiencing intense abdominal pain.
  • You’re experiencing uncontrollable nausea or vomiting.
  • You feel dizzy.
  • You cannot eat or drink.
  • You are on blood thinners (anti-coagulants).


At-home care

  • Don’t take anti-diarrhea medications without a doctor’s approval. They can complicate some infections.
  • Avoid over-the-counter pain medicines, including Aspirin and NSAIDs like ibuprofen, which can make the bleeding worse.
  • Stay well-hydrated. Drinking fluids containing sodium and potassium, such as sports drinks, and bullion can help keep your electrolytes in balance.
  • Stay well-nourished. Eating bland foods with good nutritional and caloric value is important.
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The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Dr. Le obtained his MD from Harvard Medical School and his BA from Harvard College. Before Buoy, his research focused on glioblastoma, a deadly form of brain cancer. Outside of work, Dr. Le enjoys cooking and struggling to run up-and-down the floor in an adult basketball league.

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