Black or tarry stools, a condition also referred to as melena, indicates upper gastrointestinal bleeding of the small intestine, esophagus or stomach. However, black stools can also be caused by ingesting medicines containing bismuth, lead, blueberries, iron pills and black licorice, but chemical testing rules out tarry stools, states MedlinePlus.
Issues within the esophagus, such as tears from vomiting and overgrown veins called varices, cause tarry stool. Abnormal conditions of the stomach, such as bleeding ulcer, inflammation and overgrown veins, darken the blood in the stool, says MedlinePlus.
Bright-red stool is a result of heavy bleeding in the upper gastrointestinal tract, small or large bowel, anus or rectum, says MedlinePlus. The bright-red color is also called hematochezia. Intense red color comes from anal fissures, cancer, hemorrhoids, Crohn's disease or ulcerative colitis, and intestinal infection.
Bloody stool can originate anywhere in the digestive system, from the mouth to the anus. Certain abnormalities result in either bright-red stool or tarry stool, such as abnormal blood vessels, loss of blood to the intestines, trauma or foreign body. Contact a physician for a physical exam of the stomach and rectum for bloody stool, even if hemorrhoids are suspected to be the root cause of the bleeding, according to MedlinePlus.