What Causes Ulcerative Colitis?

In This Article
View All
In This Article

Ulcerative colitis is a type of inflammatory bowel disease (IBD). It’s a chronic condition that irritates the lining of the intestines, causing inflammation and ulcers (sores). The most common symptoms are bloody diarrhea and abdominal pain.

Experts don’t know the exact cause of ulcerative colitis. However, research currently links it to immune system problems, genetics, an imbalanced microbiome, and various environmental factors. 

Abdominal pain patient woman having medical exam with doctor on illness from stomach cancer, irritable bowel syndrome, pelvic discomfort, Indigestion, Diarrhea, GERD (gastro-esophageal reflux disease)

Phynart Studio / Getty Images


While the precise cause of ulcerative colitis is unknown, experts have proposed several theories.

The Immune System

Typically, the immune system attacks pathogens such as viruses and bacteria. Pathogens cause illnesses like colds, infections, and viruses. Autoimmune disorders occur when the immune system can’t distinguish your healthy cells from these intruders, mistakenly attacking the wrong cells.

Ulcerative colitis is thought to be an autoimmune disorder. The immune system incorrectly thinks that food, good bacteria, and the cells in the colon are invaders. It attacks them, leading to inflammation, irritation, and sores in the intestines. 


A microbiome is a community of microorganisms (microbes). Microbes are tiny living things that the naked eye can not see. Examples include bacteria or fungi. 

Your digestive system, or gut, is a microbiome that contains trillions of bacteria and other microbes. Good bacteria help the body process food and regulate the immune response. Bad bacteria are harmful and cause illness.

Studies show that the microbiome in people with ulcerative colitis differs from that of someone without it. In short, they have less microbiome diversity than the gut needs to be healthy.

Experts are not sure if the change is what causes ulcerative colitis or if it occurs because of ulcerative colitis. 

Decreased Intestinal Barrier

The intestinal lining provides a mucosal barrier for the digestive tract, aids in food digestion, and helps your body absorb nutrients. It keeps food particles, bacteria, and digestive enzymes inside the intestines. Ulcerative colitis disrupts the intestinal barrier. 

With ulcerative colitis, intestinal barrier dysfunction lets particles escape from the intestines. This causes the immune system to treat them like invaders, creating inflammation. 

Is Ulcerative Colitis Hereditary?

There is a connection between ulcerative colitis and the CARDI15 gene mutation, which is a known contributor to Crohn's disease (the other type of inflammatory bowel disease, or IBD) and can cause Blau syndrome (a hereditary autoinflammatory disease primarily affecting the joints, skin, and eyes). It’s unclear if the mutation is passed through families or mutates after birth. 

Compared to Crohn’s, ulcerative colitis has less of a genetic connection. Identical twin data shows a 17% gene mutation match with ulcerative colitis and a 55% match with Crohn's. 

Scientists are trying to identify if there is a stronger genetic connection among those who develop ulcerative colitis as children. They are also investigating whether the cause of ulcerative colitis is different between children and adults.

Who Gets Ulcerative Colitis?

Studies show that some people are more likely to develop ulcerative colitis based on their:

  • Age: Ulcerative colitis can develop at any age, but the disease is more likely to develop in adolescents or young adults in their 20s and 30s.
  • Gender and sex: Ulcerative colitis occurs equally among genders. However, those assigned female at birth often report worsening symptoms leading up to their menstrual period.
  • Geographical location: Ulcerative colitis is more common in North America and areas with colder climates such as northern Europe. Prevalence is increasing in areas of India.
  • Family history: About 10-25% of those with ulcerative colitis have a first-degree relative (parent, child, or sibling) with inflammatory bowel disease (IBD).
  • Ancestry: It was previously thought that ulcerative colitis was more common in the Ashkenazi Jewish population. However, that hypothesis is fading as scientists learn more about the disease.

Risk Factors

While no single factor causes ulcerative colitis, the following risk factors can play a role.

Smoking Status

The risk of ulcerative colitis increases with smoking cessation (when someone quits smoking cigarettes). Experts are unsure of what causes this connection. 

This does not mean taking up cigarette smoking is a healthy choice or that it prevents ulcerative colitis. The risk factor is for those who already smoke and stop. 


It’s rare for those with ulcerative colitis to have a history of an appendectomy. An appendectomy is the surgical removal of the appendix, a finger-shaped pouch that projects from the colon. 

For years, scientists thought the appendix was useless. A 2021 study suggests it could play a role in the immune system and that the appendix may be a priming site for ulcerative colitis, giving UC a place for disease activity. Researchers are working to determine the connection between ulcerative colitis and the appendix.

What Goes Into The Body

A healthy intestine (gut) typically has a diverse microbiome and a healthy immune response. This balance can change based on genetics, diet, exercise, and what goes into your body.

Unhealthy foods, preservatives, and certain medications can affect the intestines. For example, some antibiotics can disrupt the microbiome in the gut (however, the benefits of taking antibiotics when needed generally outweigh the small chance of negative outcomes).

While there is no evidence that food causes ulcerative colitis, certain foods can trigger symptoms. There is evidence that a plant-based diet decreases symptoms, while processed foods increase symptoms. 

A Quick Review

Ulcerative colitis is an inflammatory bowel disease (IBD) that irritates the lining of the intestines. The exact cause of ulcerative colitis is unknown. There is a genetic connection, but experts are unclear if it is hereditary. Theories link the cause to multiple factors, including the immune system, an imbalanced microbiome, and environmental factors.

If you are concerned that you have ulcerative colitis, schedule an appointment to talk to your healthcare provider about your symptoms. They may refer you to a gastroenterologist (a doctor who specializes in diseases of the digestive tract) who can help rule out other conditions and ensure you get the tests you need to confirm a diagnosis.

Was this page helpful?
Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Lynch WD, Hsu R. Ulcerative colitis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022

  2. Kobayashi T, Siegmund B, Le Berre C, Wei SC, Ferrante M, Shen B, Bernstein CN, Danese S, Peyrin-Biroulet L, Hibi T. Ulcerative colitis. Nat Rev Dis Primers. 2020;6(1):74. doi:10.1038/s41572-020-0205-x

  3. Ishige T. Growth failure in pediatric onset inflammatory bowel disease: mechanisms, epidemiology, and management. Transl Pediatr. 2019;8(1):16-22. doi:10.21037/tp.2018.12.04

  4. Ungaro R, Mehandru S, Allen PB, Peyrin-Biroulet L, Colombel JF. Ulcerative colitis. The Lancet. 2017;389(10080):1756-1770. doi:10.1016/s0140-6736(16)32126-2

  5. Peppercorn MA, Cheifetz AS. Definitions, epidemiology, and risk factors for inflammatory bowel disease. In: Post TW. UpToDate. UpToDate; 2022.

  6. Peppercorn MA, Kane SV. Patient education: Ulcerative colitis (beyond the basics). In: Post TW. UpToDate. UpToDate; 2022.

  7. Heuthorst L, Mookhoek A, Wildenberg, ME, Bemelman WA, Buskens C J. High prevalence of ulcerative appendicitis in patients with ulcerative colitis. United European Gastroenterology Journal. 2021:9(10): 1148-1156. doi:10.1002/ueg2.12171

  8. Lagishetty V, Jacobs JP, Friedman TC. Unhealthy lifestyle and gut dysbiosis: A better understanding of the effects of poor diet and nicotine on the intestinal microbiome. Frontiers in Endocrinology. 2021:12. doi:10.3389/fendo.2021.667066

  9. Glassner KL, Abraham BP, Quigley EMM. The microbiome and inflammatory bowel disease. J Allergy Clin Immunol. 2020;145(1):16-27. doi:10.1016/j.jaci.2019.11.003

Related Articles