Why are my stools pencil thin?

Pencil-thin stools can happen for a range of reasons, and the stool shape alone does not tell you the cause.

Sometimes it’s temporary and related to things like:

• a low-fiber diet or dehydration
• constipation or changes in bowel habits
• IBS, which can affect how the bowel contracts
• hemorrhoids or an anal fissure, which can make passage narrower or more uncomfortable

Occasional pencil-thin stools are often harmless and may happen from temporary constipation or changes in what you’ve eaten.

But if the stools are persistently narrow or the change is new and ongoing, it’s important to be evaluated because it can also happen with narrowing or blockage in the colon or rectum, such as from a stricture, polyp, or tumor.

Please seek medical care promptly if thin stools come with any of these:

• blood in the stool or rectal bleeding
• unexplained weight loss
• ongoing abdominal pain, cramping, or bloating
• a persistent change in bowel habits
• nausea or vomiting

If this has been going on for more than a couple of weeks, or if you have any red-flag symptoms, it’s a good idea to see a clinician soon.