Causes of Narrow or Stringy Stools

Medically Reviewed by Minesh Khatri, MD on September 14, 2023
4 min read

Admit it: You sometimes peek at your poop in the toilet bowl after a bowel movement (BM). Have you ever noticed that your stool is narrow, long, pencil-thin, or stringy?

If your poop is narrow or stringy only once in a while, it’s no big deal. But if it happens often, it may be a sign of certain health problems.

Stringy stool could be a sign of both minor and more serious health conditions, like these:

Constipation is when you poop less than three times a week. It can have many different symptoms. While narrow or pencil-thin stool is not always a sign of constipation, it may be if your poop doesn’t normally look that way.

Constipation is usually caused by a lack of fiber in your diet or not enough exercise. Other causes include pregnancy, travel, use of some medications, and changes in your hormone levels.

When you’re constipated, your stool may be hard, dry, and difficult to pass. It may look lumpy.

Having narrow or pencil-thin BMs on occasion isn’t something to worry about. If it looks that way all the time or it gets narrower over time, it could be a concern, so let your doctor know.

If constipation is the cause of your narrow poop, you might also have these symptoms:

  • Belly cramps or pain
  • Bloating or gas
  • Lack of energy
  • Low appetite
  • Need to strain when you poop
  • Feel like you can’t get all the poop out

Simple constipation treatments include:

  • Add more fiber to your diet, at least 25 grams a day.
  • Eat more whole grains, fresh fruits, and veggies.
  • Get more physical activity.
  • Drink more fluids like water.

You may think that the easy way to treat constipation is to take an over-the-counter laxative. But if you overuse laxatives, it can make things worse. Talk to your doctor before you take any laxative, so you know it’s the right treatment for you.

If you have stool that’s suddenly stringy or poop that gets pencil-thin over time, does it mean you have cancer? Doctors used to link narrow BMs to colorectal or colon cancer. That’s because they thought that cancer in your colon caused it to become narrower, and your poop would look narrow after it passed through.

Now, they no longer think this is always the case. Gradual narrowing of your stool could be one symptom of colon cancer, but it's usually the result of other, much less serious conditions.

Ask your doctor if you need to take any tests to rule out colorectal cancer, like a colonoscopy.

If colorectal cancer is the cause of your narrow stool, you might have these other symptoms:

Colon cancer treatments include surgery, radiation, and chemotherapy.

Narrow stool could be a sign of another, rare kind of cancer: anal cancer. It’s a cancer that starts in your anus, or the outer part of your rectum where poop comes out.

Poop that changes in shape and becomes narrower is one possible sign of anal cancer, which is usually caused by infection with the human papillomavirus (HPV).

If anal cancer is the cause of your narrow bowel movements, you may have these other symptoms:

  • Pain, a “full” feeling, bleeding, or itching in your rectum
  • Strange rectal discharge
  • Lumps felt around the opening of your anus
  • Swollen lymph nodes around your anus

Anal cancer is usually treated with surgery, radiation, and chemotherapy.

Changes in your poop’s shape or size can be a sign of irritable bowel syndrome (IBS). Your stool may look smaller or narrower than normal. Its texture can change. You may have diarrhea, which can look stringy.

If irritable bowel syndrome is the cause of your narrow stool, you might also have these other symptoms:

  • Constipation
  • Gas
  • Bloating
  • Mucus in your poop
  • Strong urge to go
  • Belly cramps that ease after you poop
  • After you poop, you feel like you have to go again

To manage IBS, get more fiber in your diet. Soluble fiber in foods like fresh apples, oranges, and beans can ease constipation and diarrhea. Insoluble fiber in foods like whole grains can bulk up your stool so it passes more normally.

Stress may trigger IBS episodes, so try to find healthy ways to manage stress, like exercise.

Parasites like tiny worms can get into your gut and cause thin, stringy BMs or stringy, loose diarrhea.

These bugs are also called roundworms. They live in the soil and can get into your food, then live in your gut.

Roundworms are more common in hot, humid parts of the world, underdeveloped countries, and places where there is poor sanitation.

If roundworms are the cause of your stringy, thin poop, you may have these other symptoms:

  • Fever
  • Shortness of breath
  • Cough or wheeze
  • Belly pain
  • Nausea
  • Vomiting
  • You see actual worms in your poop

If the worms stick around in your gut for a long time, they can block your bowels. Signs of a blockage are severe belly pain and vomiting. If you have these symptoms, get help from a doctor right away.

Contact your doctor right away if you think you or your child has a parasitic infection or worms. Diarrhea can dehydrate you very quickly.

Your doctor may prescribe the drug albendazole to get rid of the roundworms and their eggs.