A person should contact his doctor immediately if he is producing tarry stools or if there are any changes to the color of stools, as advised by Medlineplus. Tarry, or bloody stools are often the result of an issue in the digestive tract. Bleeding in the small intestines, stomach and esophagus can all cause stools to become bloody or black and tarry.
If bleeding occurs in the upper part of the GI tract, it may be happening because of a foreign body, abnormal blood vessels, trauma, gastritis or bleeding ulcers in the stomach, according to Medlineplus. If stools are bright red, it usually means that the blood is originating from the anus, rectum or the large or small bowel.