What are some causes of narrow stools?

Colon cancer and irritable bowel syndrome can cause narrowing of the stool, notes Mayo Clinic. Infrequent occurrences of narrow stool are usually not serious, however.

Pencil-thin or otherwise narrow stools may result from an obstruction or narrowing of the colon due to cancer, reports Mayo Clinic. In addition, irritable bowel syndrome often causes a change in stool size and consistency. While most instances of narrow stools are benign and no cause for worry, narrower-than-normal stools that occur for longer than a couple of weeks require evaluation by a medical doctor. Narrow stool accompanied by severe abdominal pain or rectal bleeding require immediate evaluation by a medical professional.