Smooth stools may be caused by residual blood, fat or mucus in the stool, which may indicate gastrointestinal bleeding, fat metabolism disorder in the hepatobiliary system or other gastrointestinal diseases. 1. Gastrointestinal bleeding: If the patient suffers from gastrointestinal bleeding, it will lead to the phenomenon of smooth and shiny stool surface. 2. Hepatobiliary system fat metabolism disorder: If the patient has recently over-eaten greasy food or has liver metabolism disorder, it will cause insufficient bile secretion, resulting in an increase of undigested fat, which will be excreted with smooth stools. 3. Gastrointestinal diseases: when patients have gastrointestinal disorders, ulcerative colitis and other diseases, the mucus secreted by the intestinal tract will increase, which will be discharged together with the stool, showing increased mucus, and smooth stools will also occur. If the above symptoms occur, you should go to the hospital in time to find out the cause of the disease as soon as possible under the guidance of professional physicians and give targeted treatment.