Irritation of the rectum from diarrhea or constipation, a small hemorrhoid, or an anal fissure can cause a small amount of bright red blood on the surface of the stool or on the toilet paper. Hemorrhoids and anal fissures usually occur after straining during a bowel movement because of constipation. This type of bleeding can cause pain during a bowel movement and does not make the toilet water bloody. It is not serious if there is only a small amount of blood and the bleeding stops when the diarrhea or constipation stops. Home treatment is usually all that is needed.
Bleeding can occur anywhere in the digestive tract. The blood is digested as it moves through the digestive tract. The longer it takes the blood to move through the digestive tract, the less it will look like blood. Often blood that is caused by bleeding in the stomach will look black and tarry. A tarry stool has a black, shiny, sticky appearance and looks like tar on a road. Blood that has moved quickly through the digestive tract or that begins near the rectum may appear red or dark red.