What are the common causes of narrow stools?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Narrow stools, often described as pencil-thin or ribbon-like, can signal a range of underlying conditions. Common causes include obstructions in the colon or rectum, such as tumors, polyps, strictures, or scarring from inflammation. Less serious causes may involve constipation, hemorrhoids, or irritable bowel syndrome (IBS).

Because narrow stools can occasionally point to serious conditions like colorectal cancer, it's important not to ignore persistent changes in stool shape. The fastest way to understand what may be behind your symptoms — and what to do next — is to take a free, instant, online symptom check. In just a few minutes, you'll get personalized insights based on your specific symptoms, helping you decide whether to monitor at home, see a primary care doctor, or seek urgent care. Knowledge is the first step toward relief and peace of mind.

Reviewed for medical accuracy: 07/15/2026

Important Next Steps

Learn why your stools are narrow Discover if narrow stools need care Find likely causes of narrow stools See OTC options for bowel changes Find a doctor for digestive symptoms Discover home remedies for stool changes Understand if narrow stools signal serious illness

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Explanation

Narrow or pencil-thin stools might be concerning for some people. While not always a sign of a serious problem, they can sometimes indicate an obstruction in the colon.

Possible Causes:

Colonic Obstruction: An obstruction in the colon, such as a mass, can lead to narrow stools. This is because the stool has to pass through a smaller opening, resulting in a thinner shape.
Rectal Issues: Conditions affecting the rectum, like strictures or growths, can also cause stools to become narrow.

It's important to note that while narrow stools can be caused by these conditions, they are not always indicative of a serious issue. If someone experiences persistent changes in their stool shape or other concerning symptoms, they should use Ubie's free AI-powered symptom checker to better understand potential causes and determine whether professional medical evaluation is needed.

(References)

Borhan-Manesh F. (2009). "Low caliber stool" and "pencil thin stool" are not signs of .... Digestive diseases and sciences, 18683051.
Chedid V, Arasoghli M, & Hashash JG. (2015). Obstructing Colonic Mass: A Case of Recurrent .... Case reports in gastrointestinal medicine, 26199767.
Yoshizawa M, Mizukoshi N, Nadaya T, Kuwahara A, Kimura S, Usuki S, et al. (2022). [Preoperative Chemoradiotherapy for Advanced Rectal .... Gan to kagaku ryoho. Cancer & chemotherapy, 36732982.

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