Irritable Bowel Syndrome

Types of IBS

Doctors classify IBS into subtypes based on stool consistency and frequency. Knowing which type you have is important because not all types respond to the same treatments, and treatments that may help with one type can make another type worse. Still, your doctor can diagnose you with IBS even if your symptoms don’t fall into one of these subtypes.

The three subtypes of IBS are:

• IBS with constipation (IBS-C): More than a quarter of your stools are hard, and less than a quarter are loose or watery
• IBS with diarrhea (IBS-D): More than a quarter of your stools are loose, and less than a quarter are hard
• IBS with mixed bowel habits (IBS-M): With this type, you experience both watery and hard stools equally on the days that you have bowel movements.

What causes IBS?

Experts have not yet identified the causes of IBS, but they believe a combination of factors contributes. Functional GI disorders like IBS are thought to be caused by a communication breakdown between the brain and the gut. These communication problems may speed up or slow down the movement of food through your intestines, leading to diarrhea, constipation and other symptoms. Poor signaling between the brain and your gut can also make nerves more sensitive and cause them to overreact to normal digestion, triggering discomfort and other symptoms.

Other potential causes of IBS include:

• Changes to your microbiome: Your gut microbiome includes good bacteria and other microbes. People with IBS appear to have different microbiomes than people without IBS.
• Environmental factors: Stress (particularly early-life stress), food intolerances and antibiotic use have all been linked to IBS symptoms.
• Infections: IBS symptoms can develop after a severe GI infection called gastroenteritis.

Irritable bowel syndrome risk factors

IBS is very common and can affect people of all ages and races. Anyone can get IBS, but in the US, it affects more women than men and usually appears before age 45. You may be at greater risk based on your lifestyle, history of certain medical conditions and genetics.

Risk factors for IBS include:

• Being female: About twice as many women experience IBS, possibly due to hormone fluctuations.
• Having a family member with IBS: It’s not entirely clear how genetics affect IBS, but people with IBS tend to have a family member with the condition.
• Having a mental health condition: People with IBS are more likely to have anxiety, depression or post-traumatic stress disorder.
• Previous gastrointestinal infections: Bacterial gastroenteritis and other infections disrupt the gut microbiome and increase the risk of IBS.
• Stress: Abnormal nerves and hormones associated with stress can trigger irregular intestinal movement.

How is IBS diagnosed?

Generally, doctors diagnose IBS based on your symptoms and medical history. There’s no test that can diagnose the condition. However, your doctor may order tests to rule out other conditions with similar symptoms, like celiac disease, Crohn’s disease, ulcerative colitis, microscopic colitis or infectious colitis.

After other conditions have been ruled out, your doctor may use established diagnostic criteria or symptom types to identify IBS and guide treatment.

• Rome criteria. These criteria include belly pain and discomfort averaging at least one day a week in the last three months. This also usually occurs with at least two of the following: pain and discomfort related to defecation, a change in the frequency of defecation, or a change in stool consistency.
• Type of IBS. IBS is often categorized into four types based on your symptoms. This helps guide treatment:
• IBS with constipation (IBS-C)
• IBS with diarrhea (IBS-D)
• Mixed IBS (IBS-M), which includes both constipation and diarrhea
• Unclassified IBS, for symptoms that don’t clearly fit the other categories

Frequently asked questions