What is IBS? Understanding irritable bowel syndrome

Irritable bowel syndrome is a chronic functional gastrointestinal disorder — meaning the bowel works abnormally, but there's no structural damage, inflammation, or detectable disease to explain it. It's one of the most common gastrointestinal conditions, affecting an estimated 10–15% of the global population, yet it remains widely misunderstood.

"Functional" doesn't mean it's in your head or less real than a structural condition. It means the problem is with how the gut functions, not with its physical structure. The symptoms — pain, bloating, cramping, diarrhoea, constipation, or both — are completely real.

How IBS is diagnosed

IBS is diagnosed clinically — by symptoms, not by a test. Most clinicians use the Rome IV criteria: recurrent abdominal pain at least one day per week in the last three months, associated with two or more of: pain related to defecation, a change in stool frequency, or a change in stool form.

There's no single test that confirms IBS. Diagnosis often involves ruling out other conditions — coeliac disease, inflammatory bowel disease, colorectal cancer — through blood tests, stool tests, or colonoscopy, depending on age and symptom pattern.

The subtypes

IBS is classified by the predominant bowel habit pattern:

• IBS-D — diarrhoea-predominant
• IBS-C — constipation-predominant
• IBS-M — mixed, with both diarrhoea and constipation
• IBS-U — unsubtyped

The subtype matters for treatment decisions. It also isn't fixed — some people shift between subtypes over time, which is one reason tracking over months gives more useful information than a snapshot.

Why tracking symptoms helps

IBS symptoms are variable and influenced by multiple factors: diet, stress, sleep, hormones, and the menstrual cycle. It can be very difficult to identify triggers without a structured log — especially because gut transit time means symptoms often appear hours after their cause.

A symptom and food diary also helps clinically. Bringing a month of structured data to a gastroenterology appointment is significantly more useful than verbal recall. It allows a clinician to see patterns across time rather than relying on your memory of a typical week.