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Blood in stools at anytime is not normal and it is matter of worry.
Fresh blood in stool is due to bleeding in lower gastraintestinal tract i.e colon and dark tar like blood is due to bleeding in upper GI tract i.e stomach and small intestine.
Reasons for bleeding are Anal fissures, Bowel ischemia, Colon polyps or colon cancer, Diverticulosis, Hemorrhoids, Inflammatory bowel disease (such as Crohn's disease or ulcerative colitis), Intestinal infection (such as bacterial enterocolitis), Small bowel tumor, Trauma or foreign body, Vascular malformation etc
Please visit you doctor as soon as possible as loss of blood from body can lead to aneamia.
Visit a Gastrologist if possible.
Few test like stool examination , colonoscopy , barium enema
or CT scan will be required to diagnose the exact cause.