What causes IBS?

The exact single cause of Irritable Bowel Syndrome (IBS) is unknown, but research shows it is a disorder of gut-brain interaction. Rather than being caused by physical damage or structural disease in the digestive tract, IBS involves how the brain and gut talk to and influence each other.¹²³⁴⁵

Doctors and scientists have identified several key factors that work together to trigger or contribute to IBS:

1. Gut-Brain Axis Disruption

• Altered Signals: Communication between the central nervous system and the enteric (digestive) nervous system becomes out of sync.
• Visceral Hypersensitivity: Nerves in the digestive tract become overly sensitive. Normal amounts of gas, stool, or digestion can trigger severe pain, cramping, or bloating.¹²³⁴⁵

2. Abnormal Gut Motility

• Muscle Spasms: The muscular walls of the intestines contract either too strongly and quickly (causing diarrhea and cramping) or too weakly and slowly (causing hard stools and constipation).¹²³
• Serotonin Signaling: Changes in chemical messengers like serotonin—which regulates bowel movement speed—are frequently disrupted in people with IBS.¹

3. Gut Bacteria and Infections

• Post-Infectious IBS: Many people develop IBS after a severe bout of bacterial or viral gastroenteritis (food poisoning or stomach flu).
• Microbiota Shifts: An imbalance or change in the types of bacteria living in the gut can influence inflammation and gas production.
• SIBO: Some individuals experience small intestinal bacterial overgrowth, where extra bacteria build up in the small intestine.¹²³⁴

4. Stress and Emotional Factors

• Amplified Response: Stress does not cause IBS on its own, but the brain sends stronger signals to the gut during periods of anxiety, pressure, or low mood, frequently worsening flare-ups.¹²³
• Early-Life Stress: A history of difficult or stressful childhood events is statistically more common in people who develop IBS later in life.¹²

Common Triggers (Things That Flare Symptoms)

While the root causes above set the stage, specific triggers can bring on a sudden episode or symptom flare-up:

• Certain Foods: Dairy, gluten/wheat, citrus fruits, beans, cabbage, and carbonated or caffeinated drinks.
• FODMAPs: Fermentable carbohydrates that draw water into the gut and produce extra gas during bacterial breakdown.
• Hormonal Changes: Fluctuations during the menstrual cycle.¹²³

You can learn more about clinical definitions and management strategies through the Mayo Clinic Irritable Bowel Syndrome Guide or the National Institute of Diabetes and Digestive and Kidney Diseases.¹²If you'd like to narrow this down, let me know:

• What specific symptoms (like diarrhea, constipation, or pain) you or someone you know are experiencing.
• Whether symptoms started after an illness or stressful event.

I can share more targeted information or management options.

The exact single cause of irritable bowel syndrome (IBS) is unknown, as it is a complex condition driven by a disruption in how the brain and gut communicate. Rather than causing visible damage or inflammation to the digestive tract, IBS alters how the bowel functions and processes normal digestive sensations.¹²³⁴⁵

Medical experts believe a combination of biological and environmental factors contributes to developing the condition.¹

Core Biological Factors

• Gut-brain axis miscommunication. The brain and digestive tract send continuous signals back and forth. Poorly coordinated signals can cause the body to overreact to normal digestive processes, resulting in pain, diarrhoea, or constipation.¹²
• Visceral hypersensitivity. People with IBS often have oversensitive nerve endings in their bowel walls. Normal amounts of gas or stool movement that wouldn't bother most people can trigger significant pain and bloating.¹²³
• Abnormal muscle contractions. The muscles lining the intestines contract to move food along. Contractions that are too strong or fast cause gas, bloating, and diarrhoea, while weak or slow contractions lead to hard, dry stools and constipation.¹
• Changes in gut microbes. Research from the Cleveland Clinic shows that people with IBS often have different types and amounts of bacteria, viruses, and fungi in their digestive tract compared to those without it. Some patients also have small intestinal bacterial overgrowth (SIBO).¹²

Common Risk Factors & Starting Points

• Severe gut infections. According to the Mayo Clinic, IBS can develop after a severe bout of infectious diarrhoea caused by bacteria or a virus, known as gastroenteritis. Roughly 20% of IBS cases begin after a gut infection clears.
• Early life stress. The National Institute of Diabetes and Digestive and Kidney Diseases notes that IBS is more common in people who experienced severe stressors in childhood, such as physical, emotional, or sexual abuse.
• Genetics and family history. IBS tends to run in families, suggesting that a combination of inherited genes and shared family environments may increase susceptibility.¹²³⁴⁵

Causes vs. Triggers

While the factors above contribute to the underlying condition, everyday triggers cause temporary symptom flare-ups without being the root cause. Common triggers include:¹

• Certain foods and drinks. Dairy, wheat, beans, citrus fruits, carbonated drinks, and high-FODMAP foods often worsen symptoms.
• Stress and anxiety. High stress levels amplify brain-gut signalling, making the bowel more reactive.
• Hormonal fluctuations. Many women notice their symptoms worsen during their menstrual periods.¹²³⁴⁵

Are you asking out of general curiosity, or are you trying to identify potential triggers for specific symptoms? If you share what you're experiencing, I can help explain how different IBS subtypes or management options work.

Irritable Bowel Syndrome (IBS) is a condition that affects how your digestive system works, particularly your large intestine (colon). There isn't one single cause of IBS. It's thought to develop from a combination of factors affecting the communication between your brain and gut.

What causes IBS?

The main contributing factors include:

1. Gut-brain communication problems

• Your brain and digestive system constantly communicate through the gut-brain axis.
• In IBS, this communication can become disrupted, making your bowel more sensitive and reactive.
• Stress and anxiety can make symptoms worse.

2. Increased gut sensitivity

• The nerves in your intestines can become overly sensitive.
• Normal digestion, gas or bowel movements may cause pain, cramping and bloating.

3. Changes in gut bacteria

• The balance of bacteria living in your intestines (gut microbiome) may be different in people with IBS.
• This can affect digestion, gas production and bowel movements.

4. Previous stomach infections

• IBS can develop after food poisoning or gastroenteritis.
• This is known as post-infectious IBS.

5. Abnormal bowel movements

• Your intestines may contract too quickly, causing diarrhoea.
• Or they may contract too slowly, causing constipation.

6. Food sensitivities

• Certain foods can trigger symptoms, including:

  • Dairy products.
  • Onions and garlic.
  • Wheat products.
  • Beans and lentils.
  • Certain fruits.
  • Artificial sweeteners.

7. Stress and emotional factors

• Stress doesn't necessarily cause IBS, but it can trigger flare-ups.
• The gut is particularly sensitive to changes in stress hormones and nervous system activity.

Can something trigger IBS?

Yes. Some people notice their IBS begins after:

• A bout of food poisoning.
• A particularly stressful period in life.
• Antibiotic treatment.
• A stomach bug.
• Major hormonal changes.
• Changes in diet.

Is IBS permanent?

Not necessarily. IBS is usually a long-term condition, but symptoms can improve considerably with the right dietary changes, stress management and sometimes medication.

A question that might help narrow things down

Which symptoms do you experience most?

• Bloating and excessive wind.
• Constipation.
• Diarrhoea.
• Alternating constipation and diarrhoea.
• Abdominal pain or cramping.
• A combination of these.

I can explain what might be happening in your gut and what commonly helps depending on your symptoms.

One important note: IBS should not be assumed if you have unexplained weight loss, blood in your stools, persistent night-time diarrhoea or anaemia. These warrant medical assessment.