SIBO and IBS cause similar symptoms. Doctors can differentiate SIBO from IBS with breath tests or by taking a sample of fluid from your small intestines.

Irritable bowel syndrome (IBS) is a common gastrointestinal (GI) condition that can cause symptoms such as

Small intestinal bacterial overgrowth (SIBO) occurs when there are too many bacteria and other microorganisms in your small intestines. Its symptoms widely overlap with IBS and other GI conditions such as:

SIBO is commonly misdiagnosed as IBS, and the two conditions have been reported as overlapping in as many as 76% of people.

Read on to learn more about the difference between SIBO and IBS.

IBS is a functional GI condition, meaning that it’s caused by problems with your brain-gut interaction. It’s thought to affect about 12% of people in the United States. The cause isn’t known, but it’s been associated with:

IBS is further broken down into the following categories depending on which symptoms are predominant:


SIBO is an overgrowth of bacteria and other microorganisms in your small intestines. Excess bacteria can cause similar symptoms to IBS such as abdominal pain and diarrhea.

The exact cause of SIBO is still poorly understood. The upper part of your small intestines rarely contains more than 1,000 microorganisms per milliliter due to the presence of stomach acid and regular contractions of the muscular wall of your small intestines.

SIBO has been associated with conditions that reduce stomach acid production or disturbances in small intestine motility caused by:

  • connective tissue disorders
  • chronic opioid use
  • diverticulitis
  • small bowel adhesions (which are lumps of scar tissue in your bowel)
  • diabetic enteropathy

In a 2023 study, researchers estimated that the prevalence of SIBO among people with IBS was 36.4%.

IBS and SIBO symptoms are nonspecific and overlap. Many people are thought to have both conditions. Symptoms that occur in more than two-thirds of people with SIBO include:

Some people also develop:

IBS and SIBO cause overlapping symptoms.

SIBO develops in your small intestines, which is responsible for fat absorption. People with severe SIBO may develop a deficiency of fat-soluble vitamins such as:

and other nutrients such as:

SIBO symptoms are nonspecific, which makes it very easy to misdiagnose with IBS and other GI conditions.

In a 2022 review of studies, researchers found that a significant number of people referred to GI specialists with IBS symptoms had another underlying cause. Among 36 studies, the researchers estimated the prevalence of SIBO as 49% with lactulose breath tests and 19% with glucose breath tests.

Doctors primarily diagnose IBS by reviewing your symptoms and performing a physical exam. Doctors widely follow the Rome IV criteria when making a diagnosis. According to the Rome IV criteria, a diagnosis can be made if you have recurrent abdominal pain for an average of 1 day or more per week in the last 3 months associated with:

  • pain when having a bowel movement
  • changes in your bowel movement frequency
  • changes in the appearance of your stool

Your doctor may order additional tests such as blood or stool tests to help rule out other conditions.

There’s no gold standard test for SIBO. If a doctor suspects SIBO, they might recommend a carbohydrate breath test. This test involves consuming a solution containing sugar to measure levels of hydrogen and methane in your breath, which are produced by microorganisms in your gut released into your breath.

Learn more about SIBO breath tests.

Breath tests are noninvasive, cheap, and fast. Another test doctors can use to help diagnose SIBO is a jejunal aspirate culture.

During this test, doctors take a small sample of the fluid from your small intestines using a long, thin tube. This procedure is called an esophagogastroduodenoscopy (or EGD test) More than 1,000 microorganisms per milliliter is an indication of SIBO.

SIBO may lead to fat malabsorption that causes your poop to float and appear oily, smelly, or watery.

They may cause other changes such as:

  • loose, soft, and watery stools
  • mucus in your stool
  • thin and pencil-like stools
  • hard and lumpy stools

It’s important to seek immediate medical attention if your stool is bright red or tar-colored.

IBS can be treated with:

Antibiotics are the main treatment for SIBO. But, about 45% of people have recurrent SIBO within 3 months. You’ll likely be given a second course of antibiotics if your symptoms come back within 3 months.

Doctors sometimes recommend a liquid diet called the elemental diet if you don’t respond to antibiotics or if you can’t tolerate antibiotics.

Learn more about what to eat if you have SIBO.

SIBO and IBS are common GI conditions that cause similar symptoms such as diarrhea, abdominal pain, or bloating. Many people who have IBS also have SIBO.

It isn’t usually possible to tell SIBO and IBS apart based on your symptoms alone. Doctors can perform tests such as a carbohydrate breath test or a jejunal aspirate culture to help differentiate them.