Causes of ulcerative colitis

The exact cause of the condition is unknown, but researchers believe there are a number of factors involved. These are listed below.

Immune system

Some researchers believe a viral or bacterial infection triggers our body’s natural defence system against infection, the immune system.

The immune system responds to the infection by causing the inflammation associated with ulcerative colitis, but for some reason the immune system doesn’t “turn off” once the infection has passed, and continues to cause inflammation.

Other scientists think no infection is involved and the immune system just malfunctions by itself.

A leading theory is that the immune system mistakes “friendly bacteria” found in the colon (which aid digestion) as an infection. So it tries to halt the spread of what it thinks is an infection by causing inflammation (swelling) of the colon. Conditions where the immune system attacks healthy tissue are known as autoimmune conditions.


It seems that genes you inherit play a role in developing ulcerative colitis. Studies have shown around one-in-six people with ulcerative colitis have a close relative with the condition. Also, levels of ulcerative colitis are a lot higher in certain ethnic groups than in others.

Researchers have identified several genes that seem to make people more vulnerable to developing ulcerative colitis, although exactly how they do this is still uncertain.


Where and how we live also seems to play a role in the development of ulcerative colitis. The condition is more common in urban areas in northern parts of Western Europe and America.

Various environmental factors have been suggested, including:

  • air pollution
  • diet: the typical Western diet is high in carbohydrates and fats, which may explain why Asian people, who tend to eat a diet lower in carbohydrates and fats, are less affected by ulcerative colitis
  • hygiene: children are being brought up in increasingly germ-free environments, but it is possible the immune system requires exposure to germs to develop properly (this is known as the hygiene hypothesis, and has also been suggested as a possible cause for the rise in allergic conditions such as asthma)

However, no factors have been positively identified.

Comments are closed.