What Causes Thin or Narrow Stool?

thin or narrow stoolFor the majority of people, normal stool is one or two inches in diameter, so suddenly producing a thin or narrow stool can be startling. To have it happen once or twice may not be harmful, but if you have narrow, thin stools on a regular basis, it could be a sign of an underlying health problem that requires medical intervention.

So what is narrow stool? When we look at the anatomy of the colon, stool is really a thick liquid as opposed to a solid as it enters the colon. As stool makes its way into the lower colon, it absorbs water and salt to become solid. By the time it reaches the descending and sigmoid colon on the left side of the abdomen it should be solid. Narrow stools are stools that are not exactly solid — they are thin, pencil-like, or as some people describe them, “ribbon-like.”

What Are the Causes of Narrow or Thin Stools?


More often than not, a change in bowel movements has something to do with diet, but there are cases where certain health conditions can play a role in the development of narrow or thin stool.

The following outlines what causes narrow stools:


A lack of liquids and a low-fiber diet can lead to constipation. Adding fiber to your diet adds bulk to the stool, increasing its size. Many people find that if they don’t consume enough fiber, their stools become thin and stringy.

You can get more fiber by adding whole grain, such as bran and oats, to your diet. Fruits and vegetables can also increase your fiber intake.

Also read: Essential oils for constipation: Benefits, usage, and warnings


One of the most common cancers in the developed nations is colorectal cancer. Pencil thin stools are a persistent symptom of colon cancer and are accompanied by weight loss and rectal bleeding. Thin stools can also occur with anal cancer, but it’s less common.


This is a term for irritable bowel syndrome, a condition that can lead to smaller, larger, or narrower than usual stools. Some IBS sufferers experience constant, severe diarrhea while others have constant constipation. With diarrhea, the stools become thin and runny, and with constipation, the stools come out either lumpy or hard.

Also read: IBS back pain: How irritable bowel syndrome causes back pain and what to do about it

Diarrheal Illness

There are illnesses that can cause diarrhea, such as food poisoning, infections, inflammatory bowel disease (IBD), and IBS. While we think of diarrhea as watery stools, it can also be defined by having more than three bowel movements in one day. Not eating the way you normally do along with constant stool movement can lead to thinner stools.

Also read: 14 essential oils for diarrhea and various ways to use them

Colon Polyps

This is a small clump of cells that can form on the lining of the colon. Most of these polyps are harmless; however, some colon polyps can develop into colon cancer. When colon cancer is found in the later stages, it’s often fatal. The polyps are essentially growths that extend from the bowel wall and can create thin stool when they occur near the end of the colon. This is due to the fact that the growth is causing an obstruction.

Also read: Colon polyps: Diet and natural home remedies

Foreign Object

This means any object in the stomach that is indigestible and not food. Usually, foreign objects are a problem for small children. For instance, some kids swallow toys. There are also foreign objects developed within the body, such as gallstones. A large stone released from the gallbladder can cause an obstruction in the bowel, which can lead to thin or narrow stools.

Bowel Obstruction

Any blockage that keeps food or liquid from passing through the small or large intestine is referred to as a bowel obstruction. Adhesions in the abdomen, inflamed intestines, infections, hernias, and colon cancer all have the potential to cause a bowel obstruction.

Also read: Partial Bowel Obstruction: Causes, Symptoms, and Diet

Fecal Impaction

This is a hard mass of stool that becomes so hard that you can’t push it out. It is a condition that can be very serious if not addressed. The overuse of laxatives can cause fecal impaction. Fecal impaction is common in older people who have bowel issues.


An abdominal hernia can happen when an organ or a piece of tissue protrudes through a weak spot in one of the muscle walls of the abdominal cavity. A sac that bulges through the weak spot may include a piece of intestine or lining of the colon. If a portion of the bowel gets trapped within a hernia, the bowel becomes narrow. There are even severe situations where the trapped bowel gets strangled and blood supply to a section of the bowel wall is cut off.


Having volvulus means that you have a twisted bowel. It’s like a loop that obstructs fecal matter from moving through the intestines. If volvulus is not treated, it can lead to cell death since blood flow to the area is often compromised.

Volvulus occurs in about 1.7 to 6.2 percent of adults living in the western world, and may be due to adhesions, tumors, or diverticula, but research into the causes is ongoing.

Also read: Sigmoid volvulus: Causes and treatment of twisted sigmoid colon

Anorectal Stricture

Also referred to an anal stenosis, anorectal stricture means that a tubular organ has become extremely narrow and can’t perform the way it’s supposed to. With anal stenosis, the anal canal narrows, making it difficult to pass normal stool. An enlarged prostate or bladder cancer can cause an anorectal stricture.

Symptoms That May Accompany Narrow Stools

Now that we have addressed the causes of narrow stools, let’s look at the warning signs. These narrow stools symptoms are not meant to scare you. Again, there are cases where you might have a day or two of thin stool and then go back to normal fecal size and shape. You should be concerned when symptoms persist.

  • Bloody stools
  • Dizziness and confusion
  • Abdominal pain
  • Vomiting
  • Fever
  • Unexplained weight loss
  • Dehydration (dry mouth and reduced tear production)
  • The prolonged passing of thin stools

How Are Narrow Stool Causes Diagnosed?


To diagnose the cause of narrow stool, a doctor may require a fecal occult test to check for blood in the stool. A stool sample to test for the presence of bacteria or parasites may be a doctor’s focus. Some people notice a change in bowel movements if they suffer from celiac disease, so blood tests may also be used even if it is to simply rule out a condition like celiac. There are also the following tests and procedures for diagnosing the cause of narrow stool:

  • Flexible Sigmoidoscopy: Helps examine the lower colon.
  • Colonoscopy: An examination of the entire colon.
  • X-ray: Along with a contrast (barium), this provides a view of the gastrointestinal tract.
  • CT Scan: This allows for a view of abdominal organs.

If you have the occasional narrow, thin, or stringy poop, there is no reason to panic or call your doctor. If symptoms occur for more than one week and you also experience vomiting, abdominal pain, rectal bleeding, or fever, then you should see a doctor as soon as possible. As with any condition associated with narrow stool, the sooner it’s addressed, the better chance there is of a positive outcome.




Related Reading: