Ulcerative Colitis Causes: Genes, Immune System, Environment

Medically Reviewed by Neha Pathak, MD on October 18, 2022
4 min read


No one knows exactly what causes ulcerative colitis, but experts think it’s related to your genes, your immune system, and the environment. It may also be linked to changes in your gut microbiome, the collection of bacteria and other tiny organisms that live in your intestinal tract. 

Your genes appear to play a part in whether you get UC. Researchers have found variations in several genes that they think are linked to the condition. Some of these genes are thought to be involved in your immune system. Others are associated with protecting your intestines. 

You’re more likely to get UC if a relative has it. Research has found that up to 1 out of every 4 people with the condition has a family history of inflammatory bowel disease (either UC or Crohn's disease).   

Anyone can get ulcerative colitis. But some groups, including white people and those of Ashkenazi Jewish descent, are at higher risk of getting UC than others. This also suggests a genetic connection. 

Is ulcerative colitis an autoimmune disease? Many scientists think so. Autoimmune  diseases are those in which your immune system, which normally works to fight off infections, instead attacks healthy tissues in your body.

It’s not clear exactly why this happens. Your immune system might mistake helpful bacteria in your gut (the type that aid digestion) for harmful bacteria that could cause infection. This triggers an unnecessary immune reaction that leads to the colon and rectum inflammation that causes symptoms of ulcerative colitis.

Or a bacterial or viral infection might have triggered your immune system, but for some reason, your immune response didn’t stop once the infection was gone. 

A germ, like a virus in your environment, might raise your chances of getting ulcerative colitis.

If you use nonsteroidal anti-inflammatory drugs, antibiotics, or birth control pills, your chances of having it may increase slightly. It’s possible a high-fat diet is related to it, too.

A few other things could be related to the cause or might trigger a flare-up:

  • Stress
  • Emotional distress
  • Some kinds of food

Along with your genes, various things in your environment could contribute to causing UC. 

Because the condition is more common in people who live in urban areas, researchers have looked at whether air or water pollution might be a factor. They haven’t found strong evidence of this. 

But it’s clear that those who live in countries with good sanitation are more likely to get UC. This may be because they’re exposed to less bacteria, which affects their microbiome. 

Infections caused by viruses and bacteria in your environment might raise your chances of getting UC. So could using certain medications that may affect your microbiome, such as nonsteroidal anti-inflammatory drugs (NSAIDs), antibiotics, or birth control pills.

While research hasn’t produced definite answers, scientists think some of these things also could play a role in causing UC or making it worse:

  • Diet
  • Stress
  • Smoking
  • Sleep loss
  • Lack of vitamin D
  • Whether you were breastfed as an infant

Scientists know that the gut microbiomes of those with UC are different from those of healthy people. But it’s not clear whether this might be a cause or a result of the condition. 

Some research has found that people with UC had less of certain helpful bacteria in their digestive tract when they were having flare-ups.

They’ve also been found to have higher levels of other types of bacteria that promote inflammation. Their gut microbiomes are less diverse, and less stable, than those of healthy people. This unhealthy balance of gut microbes is called “dysbiosis.”

Anyone can get ulcerative colitis. But if you’re an older man, you’re at higher risk than an older woman. And even though it can strike at any age, it usually begins before you’re 30 or after 60.

If someone in your family has UC, you’re more likely to get it, too. But the majority of people with the disease don’t have a family history of it.

No. Scientists don’t really know why your immune system starts to go haywire and inflames your bowel in ulcerative colitis. What seems fairly clear, though, is that it has little to do with what you’ve done in the past. You didn’t catch UC from some infected person or from eating or drinking the wrong thing. Nor did you get it from simply being stressed out.

That said, both hard-to-digest foods and stressful situations can trigger or worsen a flare-up of UC symptoms. You can often improve your symptoms if you avoid certain high-fiber foods like uncooked veggies, nuts, and seeds as well as fatty or greasy foods like burgers and fries. Use common sense. If you find that certain foods upset your stomach, try to stay away from them.

It can also help to maintain your mental health and avoid unnecessary stress and anxiety. Proper sleep, quitting smoking, and regular exercise could also keep flare-ups at bay.