Ulcerative colitis (UC) is a chronic inflammatory condition that affects the inner lining of the colon and rectum. As one of the primary types of inflammatory bowel disease (IBD), UC causes persistent irritation and ulcers in the digestive tract. While the exact cause of ulcerative colitis remains uncertain, ongoing research continues to point toward a combination of immune system dysfunction, genetic predisposition, microbial imbalances in the gut, and environmental influences.

This article explores current scientific theories and contributing factors believed to play a role in the development of UC.

Theories Behind Ulcerative Colitis

1. Immune System Malfunction

One of the leading theories behind UC is that it stems from an autoimmune reaction. In a healthy immune system, harmful pathogens like bacteria and viruses are targeted and eliminated. However, in people with UC, the immune system mistakenly attacks the body's own tissues—specifically the cells lining the colon.

This misdirected immune response may be triggered by the presence of harmless food particles or beneficial gut bacteria, which the immune system misidentifies as threats. The result is chronic inflammation, irritation, and ulcer formation within the colon.

2. Gut Microbiome Imbalance

Your digestive system hosts a vast community of microorganisms, collectively known as the gut microbiome. These microbes include beneficial bacteria that aid in digestion, regulate immune responses, and maintain overall gut health.

In individuals with ulcerative colitis, studies have found that the diversity and balance of gut bacteria are often disrupted. People with UC tend to have fewer varieties of beneficial microbes, which may impair the gut’s ability to regulate inflammation effectively. It remains unclear whether these microbiome changes are a cause or consequence of the disease, but the correlation is strong enough to suggest a significant connection.

3. Weakened Intestinal Barrier

The intestinal lining acts as a barrier, allowing the body to absorb nutrients while preventing harmful substances like toxins and bacteria from entering the bloodstream. In people with UC, this barrier becomes compromised.

When the mucosal layer is weakened, particles that should remain in the intestines can leak into the body. This leakage prompts an immune reaction, further intensifying inflammation. This dysfunction is both a hallmark and a potential contributing cause of ulcerative colitis.

Is Ulcerative Colitis Hereditary?

There is some genetic link between ulcerative colitis and inherited traits. Specific gene mutations—such as those involving the CARD15 gene, more commonly associated with Crohn's disease—may contribute to IBD risk. However, the genetic influence in UC appears to be weaker compared to Crohn’s disease.

Studies of identical twins show that if one twin has UC, the likelihood that the other also has it is about 17%. In contrast, this figure is significantly higher for Crohn’s, where twin concordance can reach 55%. Researchers continue to study whether certain gene mutations are more common in children with UC compared to adults and whether these mutations are inherited or occur after birth.

Who Is Most Likely to Develop Ulcerative Colitis?

Ulcerative colitis can develop at any age but tends to appear more commonly during adolescence and early adulthood. A range of demographic and biological factors may influence a person's risk of developing the condition:

  • Age: Most diagnoses occur in individuals in their late teens to early 30s, although some cases can develop later in life.
  • Sex: UC affects individuals of all genders equally. However, people assigned female at birth may experience worsened symptoms around their menstrual cycles.
  • Geography: The condition is more prevalent in developed regions such as North America and northern Europe. Recent trends also show a rise in UC cases in developing countries, such as India.
  • Family History: An estimated 10%–25% of people with UC have a first-degree relative (parent, child, or sibling) with IBD.
  • Ancestry: Previously, UC was thought to be more common in individuals of Ashkenazi Jewish descent. However, this assumption is now being reconsidered as data becomes more diverse and inclusive.

Environmental and Lifestyle Risk Factors

Although no single factor is known to cause UC directly, several lifestyle and environmental exposures are linked to an increased risk or worsening of symptoms.

Smoking Cessation

Interestingly, individuals who stop smoking may be more likely to develop ulcerative colitis. While this might seem counterintuitive, researchers suggest that nicotine could have an anti-inflammatory effect on the colon lining. Still, smoking is not recommended as a treatment or preventive strategy, given its serious health risks.

Appendectomy History

People who have had an appendectomy (surgical removal of the appendix) appear to have a lower incidence of ulcerative colitis. The appendix may play a role in immune system activity in the gut. Some studies suggest that removing the appendix may reduce immune system overactivity in the colon, but this area of research is still evolving.

Dietary Habits

What you eat doesn’t cause UC, but certain foods can influence symptom flare-ups. Diets high in processed foods, artificial additives, and low in fiber may exacerbate inflammation. On the other hand, plant-based diets rich in whole grains, fruits, and vegetables are associated with symptom relief in some individuals.

Medication Use

Some medications—particularly nonsteroidal anti-inflammatory drugs (NSAIDs) and antibiotics—may increase the risk of UC or trigger symptoms by affecting the gut microbiota and mucosal lining.

The Role of the Appendix

Emerging research suggests that the appendix may play a more active role in immune function than previously thought. Once dismissed as a vestigial organ, the appendix is now believed to house immune cells and may contribute to regulating gut inflammation.

There’s growing interest in whether the appendix may serve as a reservoir for immune activity in the gut. Individuals with UC are less likely to have had an appendectomy, prompting scientists to examine whether retaining the appendix might contribute to disease development.

Can Food or Lifestyle Alone Cause UC?

There is currently no evidence that specific foods or lifestyle choices cause ulcerative colitis. However, certain behaviors may trigger symptom flares in people who are genetically or immunologically predisposed.

For example:

  • Antibiotic overuse may disrupt the balance of gut bacteria
  • High-stress levels can impact digestion and immune responses
  • Diets lacking in fiber and high in refined sugars may promote inflammation

In contrast, regular exercise, balanced nutrition, and proper stress management may help reduce flare-ups and support overall digestive health.

 

Quick Summary

Ulcerative colitis is a complex condition with no single known cause. Instead, it likely develops through a combination of immune system dysregulation, genetics, microbial imbalances, and environmental exposures.

While heredity may play a role, most cases of UC do not follow a straightforward genetic pattern. Ongoing research continues to investigate the connection between the microbiome, gut barrier function, lifestyle factors, and immune triggers.

If you are experiencing symptoms such as persistent diarrhea, abdominal pain, or rectal bleeding, it’s important to consult a healthcare professional. Early diagnosis and targeted treatment can greatly improve quality of life and reduce the risk of complications.