Irritable Bowel Syndrome (IBS) vs. Inflammatory Bowel Disease (IBD)

Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) both cause chronic abdominal pain and diarrhea, but they are two distinct diagnoses. The two conditions can have different underlying causes, affect different areas of the gastrointestinal tract, and require different treatments.

See Gastrointestinal Conditions That Cause Chronic Abdominal Pain

Irritable Bowel Syndrome (IBS)

IBS is characterized by its unpredictability and significant changes in bowel movements. Symptoms associated with IBS include:

  • Bloating
  • Gas
  • Abdominal pain
  • Constipation
  • Whitish mucous in stool
  • Diarrhea
  • A feeling of inability to completely empty the bowel

Unlike inflammatory bowel disease, irritable bowel syndrome does not lead to inflammatory tissue changes in the intestines. In addition, experts do not believe IBS increases the risk of developing colorectal cancer.


What causes IBS?
The exact cause of IBS can be different for each person that has it. Research suggests a combination of factors may lead to the development of IBS.

Based on existing knowledge, the issues that can be treated include:

  • Bacterial infection or bacterial overgrowth. IBS may be a result of a previous infection or change in bacteria growth—too much or too little—in the small intestine. An example of changes in the microbiome is small intestinal bacterial overgrowth (SIBO).
  • Food sensitivities. Certain foods will often upset the gastrointestinal system causing IBS symptoms.
  • Problems with gut-brain interaction. The nervous system and gastrointestinal tract may be communicating incorrectly, resulting in intestinal contractions that are too weak or too strong. Abnormal contractions cause food to move too slowly or too quickly through the digestive system.
  • Mental health disorders. Depression and anxiety may play a role in IBS.

Conditions that increase risk include:

  • Stressful early childhood events. Research suggests that difficult events early in life, such as physical or sexual abuse, or other severe forms of stress, may play a role in developing IBS.
  • Family history. Certain genes may make some people more susceptible to IBS.
  • Sex. The risk of developing IBS is higher in women.1
  • Age. The risk of developing IBS is higher for people under 50.1

Diagnosing irritable bowel syndrome
IBS is a clinical diagnosis based on symptoms and not on testing, which is why there is no official test to diagnose IBS. In some cases, a person may be tested for small intestinal bacterial overgrowth (SIBO), one of the common causes of IBS.

A doctor will likely take a full medical history and ask if the patient has noticed:

  • Symptoms occurring at least 1 day a week for 3 months
  • Any of the symptoms listed above, including
    • Passing stool with mucous
    • Incomplete bowel movements
    • Change in stool consistency
    • Bloating after eating

In addition to blood work, more invasive testing may be necessary to rule out other similar conditions, such as inflammatory bowel disease. These tests include a colonoscopy, x-ray, or CT scan.

Treating IBS
Treatment for irritable bowel syndrome is dependent upon the type and severity of symptoms.

Treatment for mild to moderate IBS includes:

  • Eating high fiber foods (in some cases, a high fiber diet may make a person with SIBO feel worse and is often a tip-off to the condition)
  • Exercising
  • Drinking plenty of fluids
  • Getting enough sleep
  • Working with a nutritionist to determine food sensitivities, removing the offending foods and helping create an appropriate diet.

For more severe cases of IBS, a doctor may also recommend:

  • Over-the-counter medications. These includes laxatives, such as Miralax or other natural herbal alternatives, and anti-diarrheal medications, such as Imodium.
  • Probiotics. A healthy digestive system contains 10 thousand different species of microbes. People with IBS do not have a normal balance and diversity of microbes in their GI tracts. A probiotic supplement may be prescribed to help with the imbalance.
  • IBS-specific medications. There are certain prescription medications designed specifically to treat IBS. The first is rifaximin (Xifaxan) which can treat SIBO, however, some research suggests symptoms may return in the weeks or months following treatment.2 The other medications are used to treat symptoms, including alosetron (Lotronex), eluxadoline (Viberzi), and linaclotide (Linzess).
  • Prescription medications to treat the gut-brain system. A doctor may prescribe a range of medications, including anticholinergics (Bentyl), antidepressants (Prozac, Paxil), and pain medications, such as pregabalin (Lyrica) or gabapentin (Neurontin).

All supplements and medications carry risks of side effects. Patients are advised to discuss possible side effects with their physicians and pharmacists.

Inflammatory Bowel Disease (IBD)

There are two types of inflammatory bowel disease: Crohn’s disease and ulcerative colitis. Both types of IBD involve the inflammation of the gastrointestinal tract. This inflammation can happen anywhere from mouth to anus.

Over time, the inflammation can lead to the development of ulcers. Ulcers are often responsible for gastrointestinal symptoms such as:

  • Diarrhea (with or without blood)
  • Rectal bleeding
  • Abdominal pain

Inflammatory bowel disease can also cause:

  • Weight loss
  • Joint pain
  • Fever
  • Skin rashes or lesions

These symptoms may appear with the initial gastrointestinal symptoms or show up months or years later.


What causes IBD?
The exact cause of inflammatory bowel disease is unknown. Research suggests a number of potential causes.

  • The immune system. The immune system of a person with IBD mistakes normal bacteria in the gastrointestinal tract for something unwelcomed and reacts by sending white blood cells to the area (called an autoimmune response). Although this is a normal response, it results in inflammation.
  • Family history. One study suggests that people with the greatest risk for developing either Crohn’s disease or ulcerative colitis are those who have a relative with either condition, specifically a parent or sibling.3
  • Environmental factors. Smoking, diet, oral contraceptive pills, and antibiotics have all been studied to determine their role in the development of IBD.3 While the studies have been inconclusive, many experts believe certain environmental factors can increase the risk of IBD.

How the immune system, genetics, and environmental factors possibly work alone or together to cause IBD is unclear. Research is ongoing.

Learn more about Crohn’s disease and ulcerative colitis and what makes them different on the next page.