Inflammation of the colonic mucosa can be triggered by infection, immune dysregulation, impaired blood supply, drugs or radiation.
Diet and lifestyle: High intakes of red meat, emulsifiers and sweets, together with smoking and obesity, are considered modern “Western-style” pro-inflammatory factors.
Infection: Salmonella, Shigella, Clostridioides difficile, Mycobacterium tuberculosis and Entamoeba histolytica directly invade the epithelium, causing acute diarrhoea and bloody stools.
Immune factors: Ulcerative colitis and Crohn’s disease are autoimmune disorders in which genetically susceptible individuals mount an abnormal T-cell response that continuously attacks the bowel wall.
Microbial dysbiosis: Long-term antibiotics and a high-fat, low-fibre diet reduce protective flora and increase pro-inflammatory bacteria, driving chronic inflammation.
Ischaemia: Hypotension, arteriosclerosis or thrombosis can lead to ischaemic colitis with sudden left-lower-quadrant pain and bloody diarrhoea.
Drugs and radiation: NSAIDs, aspirin, chemotherapeutic agents and pelvic radiotherapy directly injure the epithelium or induce local vasculitis.
| Category | Main mechanism | Common triggers | Clinical clues |
|---|---|---|---|
| Infectious | Pathogen invasion | Contaminated water/food, C.diff after antibiotics | Acute fever, bloody pus stool |
| Immune | Auto-immune attack | Genetic susceptibility + environmental triggers | Chronic relapses, mucus-blood stool |
| Ischaemic | Inadequate blood flow | Arteriosclerosis, thrombosis, shock | Sudden pain + bloody diarrhoea |
| Drug/Radiation | Direct toxicity or vascular injury | NSAIDs, chemotherapy, pelvic radiotherapy | Diarrhoea after drug/RT course |
| Dysbiosis | Protective ↓ pro-inflammatory ↑ | High-fat low-fibre diet, long-term antibiotics | Bloating, watery diarrhoea, recurrent |