Why Do I Have Narrow Stools?

Anyone can have narrow stools every now and again. As long as bowel movements are otherwise normal, this usually isn't cause for concern. There are a number of possible causes of thin stools that do warrant attention, however.

Narrow stools can be caused by constipation, irritable bowel syndrome (IBS), and the use of certain medications. Less commonly, thin poop can point to something serious such as colorectal cancer.

Contact your healthcare provider if you notice these stools persist for more than a week or two or you experience them more often than not.

This article discusses narrow stool and its potential causes, as well as other signs that you should seek medical attention.

What Are Narrow Stools?

Narrow stools are long and pencil-thin, rather than the normal rounded shape. They may be harder to pass, requiring you to strain or bear down more than usual.

Depending upon the cause, narrow stool may be accompanied by other symptoms, such as:

• Abdominal pain
• Weight loss
• Bloating
• Blood mixed in or on the stool

Causes of Narrow Stools

There can be many reasons for thin or narrow stools. Sometimes they happen without any known cause. When they happen frequently, the causes may range from constipation to something more serious like cancer.

Constipation

Thin stools can signal constipation. When you are "backed up," stool passes slowly through the intestines. This allows the intestines to absorb more water from the stool, making it even more difficult to pass.

If there is significant constipation, only thin amounts of stool may be able to pass through.

Increasing fiber in the diet is important for treating constipation. Staying well-hydrated can also help.

Medications may be necessary for those whose stools don’t improve enough through dietary changes or drinking extra water. These medications can include:

• Laxatives, which help stimulate the intestine to pass stool
• Stool softeners, which can make the stool easier to pass by allowing the stool to retain water and fat cells

Hemorrhoids

Internal hemorrhoids are swollen and inflamed veins in the rectum or anus that don't extend outside the body. If they are large, they can force stool into a narrow shape as it exits. Internal hemorrhoids may also cause rectal bleeding, which may be present in or on poop.

Hemorrhoid symptoms are often relieved with nonsurgical methods such as:

• Increasing water intake to rehydrate hard stool so it can pass with less straining
• Consuming more fiber or taking fiber supplements to soften the stool so it can pass more easily
• Surgery: This is considered if the hemorrhoid prolapses (extends beyond the anus) or becomes thrombosed (a clot forms in it).
  

Irritable Bowel Syndrome (IBS)

IBS can cause changes in the size and shape of your stool. It's common for people with IBS to have stool that is smaller or narrower, especially in constipation-predominant IBS.

IBS flare-ups can happen during periods of stress, which may cause narrow stools.

If your narrow stools are caused by IBS, you may also have other symptoms like constipation, gas and bloating, and bowel movement-related abdominal pain. 

IBS can often be treated with diet and lifestyle changes, such as avoiding trigger foods, eating foods that are high in fiber, and drinking plenty of fluids. In some cases, medication may be required. These could include: 

• Fiber supplements or laxatives
• Anticholinergic medications 
• Pain medication
• Certain kinds of antidepressants
  

Diverticulitis

Diverticulitis is a digestive condition in which inflamed or infected pockets have formed in the large intestine (colon). People with an advanced case could have narrow stools or very small stools that are shaped like pellets.

This happens when the condition causes the lower colon to become distorted, which can change the shape of your stool. 

When you have diverticulitis, you may also have:

• Blood in your stool, which causes it to take on a bright or dark red color or become black and tarry
• Foul-smelling stool
• Bouts of diarrhea or constipation
• The need to strain during bowel movements

Mild cases of diverticulitis are usually treated with diet changes and antibiotics. Cases of diverticulitis that are likely to cause narrow stool usually need additional treatment.

Some people with diverticulitis develop an abscess that needs to be drained. In severe cases, surgery to remove part of the intestine may be necessary.

Fecal Impaction

Fecal impaction is similar to constipation, but more significant. With an impaction, a lump of dry stool is stuck in the rectum (the bottom portion of the colon just before the anus).

This blocks the ability of other waste to move through normally. Only narrow stool may be able to pass.

Fecal impaction is treated by removing the stuck stool in the rectum. This can be done manually by a healthcare provider. They will use a well-lubricated, gloved hand to insert a finger or two into the rectum to help break up the stool so it can be removed.

Interventions such as suppositories or enemas may also be used.

Medications

Medications that slow the movement of the intestines can cause narrow stools. They can lead to constipation and possible fecal impaction, causing thin stool. Some of the medications that can do this include:

• Opioid pain medications, such as morphine or hydrocodone
• Anticholinergics, such as scopolamine or oxybutynin
• Antidiarrheal medications, if taken too often
  

Colorectal Cancer

A cancerous mass in the intestine or closer to the end, near the anus, can cause thin stools. If the mass is large enough to block the stool’s movement through the intestine, pencil-thin stool may be the only thing that is able to get by.

Other symptoms associated with colon cancer include:

• Abdominal pain
• Blood in the stool
• Unintentional weight loss

Treatment for colorectal cancer can vary, depending on how advanced the cancer has become. Surgery to remove the mass is a common procedure and may be followed by chemotherapy or radiation, or both.

Anal Cancer

Anal cancer can have many of the same symptoms as colorectal cancer, including narrow stools. This type of cancer begins in the cells around or inside the opening of the anus.

With anal cancer, you may also have:

• Bleeding and/or pain from or around the anus
• Anal itching
• Changes in bowel habits, such as more or fewer bowel movements
• Straining during bowel movements
• A lump or mass on the anal opening
• Unusual discharge from the anus

Like other cancers, anal cancer may be treated with a combination of radiation and chemotherapy or surgery.

Are There Tests to Diagnose the Cause of Thin Stools?

A healthcare provider may recommend tests to help determine the cause of thin stools. Tests that may be done to look for the cause of thin stools can include:

• Digital rectal examination: A healthcare provider performs this manual exam to see if they can feel a mass inside the rectum.
• Stool tests: A sample of stool is sent to a lab and can be analyzed for infections or blood.
• Colonoscopy: During this procedure, a camera is inserted into the colon to look for any areas that may be abnormal or causing the symptom of thin stool. If something looks abnormal, a biopsy (sample) can be taken for testing.

When to See a Healthcare Provider 

The occasional episode of thin stool is likely not a cause for concern. However, if thin stools occur more frequently over a period of one or two weeks, notify a healthcare provider.

You should also notify your healthcare provider if your narrow stools aren't responding to what you’re doing to improve them (such as increasing fiber) or are accompanied by other symptoms, such as abdominal pain or weight loss. Blood in the stool is always a reason to talk to a healthcare provider.

Addressing the underlying condition early can help prevent complications like complete bowel obstruction or further growth and spread of cancer. 

Summary 

Occasional narrow stools are not usually concerning. When narrow stools are happen often or persist longer than a week or two, they may have causes that range from constipation to cancer. See your healthcare provider.

Narrow stools accompanied by other symptoms, such as blood in the stool or abdominal pain, should also be evaluated. Tests can be done to help find the cause.