A small amount of bright red blood on the surface of the stool is
usually caused by irritation of the rectum or a small tear in the opening at
the end of the rectum (anus). A moderately large amount of blood in the stool
often means there is bleeding in the digestive (gastrointestinal) tract between
the esophagus and the rectum, caused by inflammation, irritation, infection, or
structural problems of the digestive tract.
Irritation may occur after several loose bowel movements. It is
not serious if there is only a small amount of blood and the bleeding stops
after the bowel looseness is controlled. Passing a hard stool can also cause a
tear in the anus or irritate hemorrhoids, causing a small amount of bleeding
that stops in a short time.
Bloody stools may occur as one large, bloody bowel movement or
several bowel movements containing a moderate amount of blood (enough to turn
the water in the toilet bowl red). Depending upon where the blood is coming
from and how quickly it is moving through the digestive system, the blood may
be bright red, reddish brown, or black and tarry. If the site of the bleeding
is above the rectum, the blood will be mixed in with the stool.