When You See Blood in Your Stool

What Causes It and How to Know If It's an Emergency

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Reaching for toilet paper
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Having blood in your stool can be terrifying. And your first worry may be that you have cancer. What does it mean if you have rectal bleeding and what are some of the causes?


You may notice blood in the toilet or on the tissue after wiping. This blood can be many different colors and it can be caused by many different conditions. The important thing is not to panic, but also not to ignore your symptoms.

Most of the time, if you have blood in your stool, you will have time to consider several questions and to schedule an appointment with your doctor. However, you should call 911 or go to the emergency room if:

  • You notice large amounts of blood that's either bright red or a dark color that looks more like coffee grounds.
  • You feel lightheaded, dizzy, or confused.
  • You feel your heart racing or you find it hard to catch your breath.
  • You experience any chest pain.
  • You're worried and you have a bad feeling that your bleeding could be an emergency. Trust your instincts.


The most common causes of blood in stool are anal fissures or hemorrhoids. Even if you are aware of hemorrhoids or a fissure, though, it's important to get checked out.

It's not uncommon for people to have more than one condition causing their bleeding. And the only way to know for sure is to be evaluated by your doctor. Some non-cancerous causes of blood in stool include:

  • Hemorrhoids: Internal hemorrhoids are the number one cause of rectal bleeding and are essentially dilated veins that are found within the rectum. Depending on their size or "grade," these may protrude from the rectum. Thrombosed hemorrhoids or external hemorrhoids are due to a clot in a vein on the outside of the rectum. Unlike internal hemorrhoids, these can be quite painful.
  • Anal fissures: Anal fissures are tears in the anus and can be acute or chronic. They usually cause bright red blood on toilet tissue and can be both itchy and painful.
  • Diverticulosis and diverticulitis: Diverticulosis refers to out-pouching pockets in the colon. This condition becomes diverticulitis when these pockets become inflamed or infected. Together, they are referred to as diverticular disease. Diverticular disease is very common and can cause rectal bleeding. With diverticulitis, people can develop abdominal pain so severe that it has been nicknamed "left-sided appendicitis" and can be accompanied by a fever and chills.
  • IBD: Inflammatory bowel disease, such as ulcerative colitis or Crohn's disease, can cause bleeding (especially ulcerative colitis).
  • Peptic ulcer disease and gastritis: Peptic ulcer disease occurs when painful sores develop in the lining of the stomach or the duodenum (part of the small intestine).  Gastritis is the inflammation of the stomach lining. 
  • Esophageal tears and ulcers: These conditions affect the part of the body that attaches the throat to the stomach.


The color of the blood can give insight into where the bleeding is coming from. This can help make a diagnosis. Consider the following:

  • Bright red bleeding usually indicates bleeding from the rectum and the lower end of the colon (the left side of the colon).
  • Bleeding in the upper colon (the right side of the colon) and small intestine usually causes dark red, brown, or black bloody stools.
  • Bleeding from the upper gastrointestinal tract, such as the stomach and esophagus, tends to cause dark, coffee ground-appearing stools (melana).

Cancer Risk

Most likely, the blood in your stool—something doctors call hematochezia—is related to a less serious condition. However, if bleeding is cancer-related, colorectal cancer and anal cancer are two types of cancers that can cause blood to be present in the stool. It is important to note that precancerous conditions, like colon polyps, can also cause rectal bleeding. But do not assume that because you have blood in your stool you have advanced cancer.

Blood in stool that is caused by cancer may be associated with other symptoms as well. Some of these include fatigue, abdominal pain, pencil-like thin stools, and unintentional weight loss (or a loss of more than 5% body weight over a six- to 12-month period).

Here's additional information about the two types of cancer that are associated with bloody stool.

  • Colon Cancer: Colon cancer is the third leading cause of cancer deaths in men and women. These cancers can cause blood in stools, with the type of blood varying by the location of the cancer. Cancers on the right side are more likely to have dark, tarry stools. Those on the left side are more likely to present with bright red blood. A family history of colon cancer raises the risk, but many people who develop colon cancer do not have any history of the disease in their families. Other symptoms of colon cancer may include abdominal pain or bloating.
  • Anal Cancer (Rectal Cancer): Anal cancer can cause bright red bleeding and other symptoms, such as itching or a bump in the anal region that can easily be confused with a hemorrhoid.

Foods and Medications

Medications or foods can also alter the color of stools. Bismuth subsalicylate (Pepto-Bismol) and Kaopectate can cause black stools following usage. Iron tablets and eating beets can also cause stool color changes that are not serious.


It is important to see your doctor if you have blood in your stool. Do not assume that it is caused by hemorrhoids or anal fissures. While these are the most common culprits, you can't determine the cause at home. Colon cancer and rectal cancer are both most treatable in the earlier stages of the disease, so it's best to play it safe and always have a physician evaluate you.

View Article Sources
  • American Society of Colon and Rectal Surgeons. Colorectal Diseases and Treatments. 03/28/16.
  • Qayed, E., Dagar, G., and R. Nanchal. Lower Gastrointestinal Hemorrhage. Critical Care Clinics. 2016. 32(2):241-54.