Changes in the size and shape of stool
Each person has their own size, shape and consistency of stool. It is the change in stool pattern that matters more than the absolute size and shape of stool. Narrow stool, sometimes called pencil-thin, may occur occasionally and is of no concern. People with irritable bowel syndrome may develop thinner stools.
Nevertheless, a person with "normal" stools that has a new change in the diameter, length, width (caliber) of the bowel movement should consult his/her doctor. This may be a sign of a narrowed or scarred colon, perlhaps due to a tumor, but the doctor may want further information about accompanying symptoms or tests.
It is not unusual to have two or even three stools in a morning. The first stool will usually have a more solid form because it has been in the colon (where water is absorbed) the longest. The second stool will be looser, and if there is a third stool it will be loosest of all. Another change in stool form that often requires evaluation is the development of looser or firmer than normal stools. At one end of the spectrum is constipation or diarrhea, but even if the change does not reach these levels, consistent, milder changes in either direction need to be evaluated.