Colon cancer can cause pencil shaped stools. So can irritable bowel syndrome.

And therein lies the problem when you see skinny poops coming out of you that resemble a pencil shape or how toothpaste looks like coming out of the tube.

Let’s take a closer look at how pencil shaped stools from irritable bowel syndrome might appear different from flattened narrow bowel movements caused by colon cancer.

“The occasional narrow stool is not of major concern,” begins Santosh Sanagapalli, MD, a consultant gastroenterologist, endoscopist and colonoscopist.

“However, a persistent narrowed stool, for example of pencil thickness, can sometimes occur due to narrowing or obstruction of the colon from a colon cancer.

“The problem is that changes in the stool form or shape can also be a common feature of irritable bowel syndrome.”

This is caused by colon contractions or spasms.

Appearance of Skinny Bowel Movements from Colon Cancer vs. Irritable Bowel Syndrome

Dr. Sanagapalli explains, “Based on the appearance of the stool alone, one cannot differentiate between a benign cause such as IBS and a concerning cause such as bowel cancer.”

The stools from either condition will look the same as they are voided and also as they end up in the toilet bowl.

“Further, IBS is a far more common condition than colorectal cancer,” continues Dr. Sanagapalli.

What should you do?

“The decision to investigate further is based on any concurrent symptoms and the patient demographic.

“For example, in a young woman who describes changed (narrowed) appearance of the stool but no bleeding, weight loss, anemia or abnormal findings on examination, then the diagnosis is likely to be IBS.

“However, in an older male who describes such a change in his stool appearance along with rectal bleeding or other concerning features such as anemia or weight loss, there would be much higher concern for colorectal cancer.

“The symptom therefore requires careful evaluation by a gastroenterologist (both history, physical examination and blood tests) to decide on the likely diagnosis and need for further investigation.”

Further investigation would likely mean a colonoscopy.

Dr. Sanagapalli is a gastroenterologist and director of the Esophageal Disorders Center at St Vincent’s Hospital, Darlinghurst. He performs diagnostic and therapeutic endoscopic procedures, and enjoys providing comprehensive and holistic care to patients with a wide variety of disorders affecting the gastrointestinal tract.
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.