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What are the main causes of ulcerative colitis?

Medically reviewed by Philip Thornton, DipPharm. Last updated on Aug 22, 2023.

Official answer


The exact causes of ulcerative colitis, a type of inflammatory bowel disease (IBD), are not yet well understood. There are several main factors that appear to play a role in the development of ulcerative colitis including:

  • Abnormal immune response
  • Genetics
  • Microbiome
  • Environmental factors

Abnormal immune response

The immune system helps to protect the body against infection, releasing white blood cells to destroy invaders. This process causes inflammation - redness and swelling - in the affected area, which subsides once the infection is dealt with.

It is thought that an abnormal immune response contributes to the development of ulcerative colitis and several theories have been suggested.

It may be that the immune system attacks the good bacteria that is involved in digestion, leading to inflammation in the rectum and colon.

It has also been suggested that it may be a problem with the immune system not ‘turning off’ after dealing with an infection, resulting in chronic inflammation, ulcers, thickening of the intestinal wall and other symptoms.

Another possible cause that has been put forward doesn’t involve an infectious agent at all, but suggests that an immune system malfunction could be a cause of ulcerative colitis.


Ulcerative colitis can run in families and certain genes are thought to increase the risk a person will develop the condition. About 30 genes linked to ulcerative colitis have been identified.

Research has shown that if you have a first-degree relative with ulcerative colitis your risk of developing the condition is four times higher than that of the general population.

It’s also more common in people from certain ethnic backgrounds to develop the condition. A higher incidence of ulcerative colitis seen in the Jewish population, for example.

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The microbiome - microorganisms including bacteria, viruses and fungi - that help with digestion have been found to be different in people with IBD compared with those who don’t have such a condition.

An imbalance between the good and bad bacteria in the bowel is a possible contributing factor when it comes to ulcerative colitis.

Environmental factors

Environmental factors - a person’s surroundings and factors outside their body - are thought to play a role in the development of ulcerative colitis. How environmental factors (such as diet, medication and pollution) interact with the immune system, genes and a person’s microbiome to potentially cause ulcerative colitis are being studied.

Research has suggested there may be a link between the use of the acne medication isotretinoin (Absorica, Amnesteem, Claravis, Myorisan, Sotret, Zenatane) and ulcerative colitis, but it is still unclear whether taking isotretinoin can actually cause ulcerative colitis.

More research is still needed to uncover the environmental factors that may play a role in causing ulcerative colitis, but what we do know is that ulcerative colitis seems to be more common in countries with improved sanitation and reduced exposure to bacteria.

Factors that may aggravate your symptoms if you have ulcerative colitis

  • Stress
  • Food sensitivities
  • Alcohol
  • Nonsteroidal anti-inflammatory drugs

Previously it was thought that a stressful lifestyle or certain food sensitivities might cause ulcerative colitis, but research has not found this to be the case. Although they don’t cause ulcerative colitis, stress and food sensitivities may aggravate symptoms in some patients.

Drinking alcohol is another factor that doesn’t cause ulcerative colitis, but it can also make the symptoms worse. Use of nonsteroidal anti-inflammatory drugs, such as ibuprofen (Advil, Motrin IB) and naproxen (Aleve), may also aggravate symptoms.


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