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Are Thin Stools a Symptom of Colon Cancer?

If You Have Thin Stools, Talk to Your Doctor


Updated May 30, 2014

Having thin stools and other changes in your bowel movements from time to time is nothing to worry about, so long as these changes don't last longer than a week or two, and aren't accompanied by other symptoms that can signal something more serious, such as colon cancer. Many things can affect bowel movements including changes in your diet and exercise routine, medications, traveling, and dietary supplements. Nobody has perfectly consistent bowel movements at all times.

When Should You Be Concerned About Thin Stools?

The time to be concerned is when thin stools last longer than two weeks, are accompanied by other symptoms of something more serious, such as colon cancer or inflammatory bowel diseases, or you just don't feel well otherwise. You know your own body; if you don't feel well, you should see your doctor

Thin Stools and Colon Cancer

When stool enters the colon, it is more liquid than solid. At this stage, this thick liquid, which is roughly the consistency of a milk shake, can flow around blockages and through narrow areas. As waste moves lower in the colon, toward the rectum and anus, water is absorbed from it, and stool becomes more solid. The further along in your colon it travels, the more solid stool becomes.

The stool becoming more solid inhibits its ability to get around blockages and narrow areas. A tumor in the middle to lower portions of the colon, or in the rectum, can make it difficult for stool to pass by.

In order for the stool to pass, it is squeezed into a thinner, longer form, sometimes referred to as pencil stools. In this way, the thin, long stool can be an indication that the area through which it must pass to exit the body is smaller than it should be, hinting at the possibility of a tumor or other blockage.

See Your Doctor About Thin Stools If:

  • Three or more days have passed since your last bowel movement; two days if you have used a laxative
  • You have thin stools for two or more weeks -- either the entire two weeks, or off and on (You know your body, so seek medical attention sooner if you don't feel well.)
  • You see blood in or on your stool
  • Your thin stools are accompanied by other symptoms that indicate a more serious condition, such as other changes in bowel habits, constipation, diarrhea, or abdominal bloating
  • You have persistent cramps, severe abdominal or rectal pain and/or bloating
  • You are vomiting in association with constipation or for longer than a day or two
  • You are frequently or regularly constipated


American Cancer Society. How is Colorectal Cancer Diagnosed? Accessed July 21, 2009. http://www.cancer.org/docroot/CRI/content/CRI_2_2_3X_How_is_colorectal_cancer_diagnosed.asp

Medline Plus Medical Encyclopedia. Constipation. Accessed July 22, 2009. http://www.nlm.nih.gov/medlineplus/ency/article/003125.htm

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