Causes & Symptoms

Crohn's and Colitis UK

We don’t know yet what causes Microscopic Colitis. It’s thought that a combination of factors trigger the body’s immune system to attack healthy cells in the lining of the colon. 

These include:

  • Damage to the lining of the gut – this may be by caused by viruses, bacteria or certain medicines.
  • Genes a person has inherited. 
  • Other factors such as smoking, age and gender. 


The main symptom of Microscopic Colitis is ongoing watery diarrhoea. This is where you pass watery or loose poo more than three times a day for longer than four weeks. For some people this can be as many as fifteen times during the day and night. It may begin suddenly or gradually, can happen at any time and may be every time you go to the toilet or only now and then. 

The diarrhoea may:

  • be sudden – you may not always reach the toilet in time 
  • be explosive - this is when your rectum has more watery poo and gas than it can hold and it expels the poo with lots of force, often loudly
  • happen several times a day and at night.

There usually isn’t any blood in the poo. Other symptoms can include:

  • pain in the tummy area – which may be cramping or dull
  • fatigue or extreme tiredness – this may be caused by getting up at night to go to the toilet, but many people experience this even if they sleep through the night
  • joint pain
  • bloating and wind
  • weight loss. 

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