What Causes Rectal Bleeding And Blood In Stool?

My 21 year old daughter has had blood in her stools and now even when she doesn t have a bm she is bleeding from her anus. (She said about a teaspoon of blood today.) She has had a colonoscopy and everything looked fine. (She is allergic to nuts and fish.) What could be the cause of this? Should she see a doctor about the anal blood immediately? She has an appointment in April. In the past she has had severe stomach aches but presently she isn t in pain. She was treated for a stomach infection when she visited Peru two years ago but that appears to be cleared.