What are the primary causes of thin stools?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Thin, narrow stools are often a sign of bowel dysfunction and can occur in conditions like fibromyalgia or hemorrhoids. Other possible causes include constipation, anal fissures, or narrowing of the colon. Because thin stools can sometimes signal a more serious underlying issue, it's important to identify the root cause early.

The fastest way to understand what may be behind your symptoms is to take a free, instant, online symptom check. It only takes a few minutes, requires no sign-up, and provides personalized insights based on your specific symptoms — helping you decide whether home care, a doctor's visit, or urgent attention is your best next step.

Reviewed for medical accuracy: 07/15/2026

Important Next Steps

Learn why thin stools may be happening Discover if your thin stools need care See what could cause your narrow stools Find OTC options for thin stools relief Find a doctor for stool changes Explore home remedies for thin stools Understand if thin stools need urgent care

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Explanation

Thin stools, sometimes called "pencil thin stools," can be linked to different bowel issues. According to the references provided, bowel dysfunction is a common cause of thin stools. For example, people with fibromyalgia may experience bowel problems, which can lead to changes in stool shape and size.

Additionally, individuals with hemorrhoids may also notice changes in their bowel habits, including the presence of thin stools. Hemorrhoids can cause discomfort and may alter normal bowel movement patterns.

It's important to note that thin stools are not necessarily a sign of a serious condition, but they can indicate changes in bowel habits that may need attention. If you have concerns about your bowel movements, you can check your symptoms with our free AI-powered tool or speak with a healthcare professional for further advice.

(References)

Borhan-Manesh F. (2009). "Low caliber stool" and "pencil thin stool" are not signs of .... Digestive diseases and sciences, 18683051.
Triadafilopoulos G, Simms RW, & Goldenberg DL. (1991). Bowel dysfunction in fibromyalgia syndrome. Digestive diseases and sciences, 1985007.
Johannsson HO, Graf W, & Påhlman L. (2005). Bowel habits in hemorrhoid patients and normal subjects. The American journal of gastroenterology, 15667500.

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