Blood can show up in a person's stool as bright-red blood or as dark-red to black, tarry stool, states Cancer Research UK. Hemorrhoids may cause bright-red blood to appear in a person's stool, while bleeding in the digestive tract may appear as black, tarry stool.
Any type of blood in the stool needs to be checked out by a doctor, states Cancer Research UK. While bright-red blood often signifies hemorrhoids, it may also be indicative of rectal cancer. Patients who have bleeding somewhere in their digestive system may have bowel movements that appear black, soft and sticky. When this occurs, patients need to alert their doctors immediately.