Blood in the stool can be bright red, maroon in color, black and tarry, or occult (not visible to the naked eye). Causes of blood in the stool range from harmless, annoying conditions of the gastrointestinal tract such as hemorrhoids and anal tears (anal fissures) from straining against hard stools with constipation to serious conditions such as cancer. Blood in the stool should be evaluated by a health care professional.
Rectal bleeding (known medically as hematochezia) refers to passage of bright red blood from the anus, often mixed with stool and/or blood clots. Most rectal bleeding comes from the colon, rectum, or anus and can be associated with diarrhea. The color of the blood during rectal bleeding often depends on the location of the bleeding in the gastrointestinal tract. Generally, the closer the bleeding site is to the anus, the blood will be a brighter red. Thus, bleeding from the anus, rectum, and the sigmoid colon tend to be bright red, whereas bleeding from the transverse colon and the right colon (transverse and right colon are several feet away from the anus) tend to be dark red or maroon colored.
In some patients, bleeding can be black and "tarry" (sticky) and foul smelling. The black, smelly, and tarry stool is called melena. Melena occurs when the blood is in the colon long enough for the bacteria in the colon to break it down into chemicals (hematin) that are black. Therefore, melena usually signifies bleeding is from the upper gastrointestinal tract (for example, bleeding from ulcers in the stomach or the duodenum or from the small intestine) because the blood usually is in the gastrointestinal tract for a longer period of time before it exits the body. Sometimes melena may occur with bleeding from the right colon. On the other hand, blood from the sigmoid colon and the rectum usually does not stay in the colon long enough for the bacteria to turn it black. Rarely, massive bleeding from the right colon, from the small intestine, or from ulcers of the stomach or duodenum can cause rapid transit of the blood through the gastrointestinal tract and result in bright red rectal bleeding. In these situations, the blood is moving through the colon so rapidly that there is not enough time for the bacteria to turn the blood black.
Sometimes, bleeding from the gastrointestinal tract can be too slow to cause either rectal bleeding or melena. In these patients, bleeding is occult (not visible to the naked eye). The blood is found only by testing the stool for blood (fecal occult blood testing) in the laboratory. Occult bleeding has many of the same causes as rectal bleeding and may result in the same symptoms as rectal bleeding. It is often associated with anemia that is due to loss of iron along with the blood (iron deficiency anemia).
Causes of rectal bleeding include hemorrhoids, anal fissure, proctitis, Crohn's disease, diverticulosis, ulcerative colitis, rectal ulcer, rectal prolapse, ischemic colitis, angiodysplasia, rectal trauma, anal cancer, colon cancer, proctitis from radiation therapy, and others.
For more information, please see the colon cancer screening and fecal occult blood test articles.
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.
Causes of Rectal Bleeding
H. pylori (Helicobacter Pylori ) Infection Symptoms, Test, Treatment
Helicobacter pylori (H. pylori) is a bacteria that causes chronic inflammation (gastritis) of the inner lining of the stomach,...
Amebiasis (Entamoeba histolytica Infection)
Amebiasis is an infection caused by an amoeba. Signs and symptoms include bloody stools, abdominal pain, weight loss, fever, and...
Anal cancer, cancer located at the end of the large intestine, has symptoms that include anal or rectal bleeding, anal pain or...
An anal fissure is a small tear or cut in the skin lining of the anus. Pain and/or rectal bleeding during bowel movements are...
Colitis (Symptoms, Types, and Treatments)
Colitis refers to inflammation of the inner lining of the colon. Symptoms of the inflammation of the colon lining include...
Colon cancer is a malignancy that arises from the inner lining of the colon. Most, if not all, of these cancers develop from...
Colon Polyps (Symptoms, Causes, Types, Treatment, Prevention)
Colon polyps are common growths on the inner lining of the colon. Colon polyps may become cancerous. There are several different...
Crohn's Disease (Symptoms, Causes, Diet, Treatment, Life Expectancy)
Crohn's disease is a chronic inflammatory disease, primarily involving the small and large intestine, but which can affect...
Crohn's Disease vs. Ulcerative Colitis (UC): Differences and Similarities
Crohn's disease and ulcerative colitis are diseases that cause inflammation of part of or the entire digestive tract (GI)....
Diverticulitis (Diverticulosis, Diverticular Disease)
Most people with diverticulosis have few if any symptoms at all. When people do experience signs and symptoms of diverticulosis...
Gastroesophageal Junction Adenocarcinoma
Gastroesophageal junction adenocarcinoma is cancer that forms in the area where the esophagus joins the stomach. Having GERD and...
Hemorrhoids (Causes, Symptoms, and Treatments)
Hemorrhoids (piles) are swollen veins in the rectum and anus. Causes include pregnancy, obesity, diarrhea, low-fiber diet, and...
Idiopathic Thrombocytopenic Purpura (ITP)
Idiopathic means that the cause of the condition isn't known. Thrombocytopenic means there's a lower than normal number of...
Internal Bleeding (Symptoms, Signs, Causes, Treatment)
Internal bleeding occurs when an artery or vein is damaged and blood to escapes the circulatory system and collects inside the...
Is C. diff (Clostridium difficile) Contagious?
C. diff, or Clostridium difficile, is a bacteria that infects the colon. C. diff bacteria can be found on furniture, bathroom...
Is Cancer Contagious?
Cancer is an abnormal growth of cells. A variety of parasites and viruses have been linked to various cancers. Cancer may...
Is Colitis Contagious?
Colitis is a term that us used to describe inflammation of the colon. The terms enteritis, proctitis, and inflammatory bowel...
Is H. pylori Contagious? Symptoms and Tests
H. pylori (Helicobacter pylori) infection: Is it contagious? H. pylori infection is caused by fecal contamination in either food...
Peptic Ulcer (Stomach Ulcer)
Peptic or stomach ulcers are ulcers are an ulcer in the lining of the stomach, duodenum, or esophagus. Ulcer formation is related...
STDs in Men
Sexually transmitted diseases (STDs) are infections transmitted during sexual contact. They may be caused by viruses, bacteria,...
Though the cause of stomach cancer is unknown, risk factors for stomach cancer include diet, H. pylori infection, smoking age,...
Yellow fever is an infectious disease transmitted by infected mosquitoes. Side effects are rare with the yellow fever vaccine....
Other Causes of Rectal Bleeding
- Esophageal Varices
Examples of Medications for Rectal Bleeding
- hydrocortisone, rectal suppository, enema, foam, Cortifoam, Anusol-HC, Anucort-HC, Proctocort