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May 23, 2024

Crohn’s vs. Ulcerative Colitis: What’s The Difference?

Knowing the difference between Crohn's disease and ulcerative colitis is important for effective management. Explore the unique differences now.
Medically Reviewed
Written by
Laura Dean
Medically Reviewed by
Dr. Anshul Gupta

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Ulcerative colitis (UC) and Crohn’s disease (CD) are known as inflammatory bowel diseases. You may already be aware of some differences and commonalities between these two conditions. However, understanding their unique characteristics is essential for managing your illness. This article will review critical similarities and differences in Crohn’s vs. UC.

What Is Inflammatory Bowel Disease?

Inflammatory bowel disease (IBD) is a health condition marked by physical changes and signs of inflammation in the gastrointestinal (GI) tract. It is a lifelong, chronic disease with symptom-free periods and flare-up periods. Active disease “flare-ups” are connected to tissue and organ damage and impaired intestinal tract functioning. The condition carries several risks, including increased chances of colon cancer, potential need to surgically remove affected portions of the intestines, and possible disease complications throughout life. Diagnosis most commonly occurs between the ages of 15 and 30.

purple and green textural microphotography

Risk and Development

The development of IBD involves a combination of inherited and environmental risk factors that trigger changes in the intestinal tract. There are over 200 genetic markers that are associated with IBD, of which 70 are specific to CD. The genetic differences in those with IBD include changes in genes responsible for increased gut lining permeability and immune cell balance between pro-inflammatory and anti-inflammatory immune functions, especially in the protective mucosal lining of the intestines. (Source, Source)

While previous understanding of genes and family history may have led us to believe there was nothing we could do about disease development, we now know that you can affect gene expression. Genetic differences can also provide information for more personalized interventions.

Diet is a known environmental trigger influencing gene expression and intestinal microbial balance. Intake of excessive animal fat and dietary sulfur as a food preservative is associated with an increased risk of UC. Regular fast food intake has been associated with CD, likely due to inflammatory fats and sugars. Several nutrients are protective against IBD, including magnesium and vitamin C. (Source)

What Are the Symptoms of Inflammatory Bowel Disease?

Both UC and CD can cause symptoms that include diarrhea, blood in the stool, weight loss, abdominal pain, fatigue, fever, anemia, and growth challenges in children. An estimated 25%-40% of people with IBD experience symptoms outside the GI tract, including inflammation of the skin and eyes.

Key symptoms of UC include blood in the stool and having an urgent need to defecate, while the most common symptoms for CD include right lower quadrant abdominal pain, diarrhea, and fatigue. It is important to note that symptoms can vary from person to person, and symptoms alone don’t provide enough information to determine disease activity and inflammation.

While most symptoms overlap between the two conditions, the onset of symptoms is usually gradual in UC and sudden in CD. (Source, Source, Source)

Crohn’s vs. UC: Which Is Which?

About 3.1 million people in the United States are estimated to live with IBD. While CD is slightly more common than UC, especially for those who have family members with the condition, about 15% of those with symptoms, signs, and evidence of IBD are diagnosed with indeterminate colitis, or IBD that is not clearly one or the other. (Source)

The main differences between UC and CD are invisible to the eye, at least from outside your body. Significant differences between these conditions can better be seen and evaluated through endoscopy, a somewhat invasive way to look at the lining of your gastrointestinal tract. Colonoscopy, in which a flexible tube is inserted through the rectum, is a standard endoscopic procedure to determine if you have IBD and to provide clues about which type. The presence of a fistula, or abnormal channel between the GI tract and another organ, and inflammation beyond the colon are also clues to a diagnosis of CD. (Source, Source)

the difference between crohn's and ulcerative colitis infographic

Diagnosis and Severity Criteria

Diagnosis of IBD can involve various assessment tools, including endoscopic imagery, biopsies, clinical signs and symptoms, and laboratory tests. While the location and pattern of inflammation in the GI tract can help distinguish between CD and UC, characteristic patterns may be present in some people but not others. (Source)

A standard clinical tool for determining UC disease severity is the UC Mayo Score, which uses a scale of 0 to 12 to score findings from endoscopic imaging, symptoms including stool frequency, and whether blood is in the stool. (Source)

The Crohn’s Disease Activity Index scores symptoms on a scale of 0 to 600, with active disease indicated when the score is above 150. It includes scores for stool frequency, abdominal pain, presence of complications (e.g., fistulas, abscesses, fever, symptoms outside the GI tract such as eye or joint inflammation), and weight changes. (Source)

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GI Tract Location

The location of inflammation in your GI tract most often indicates the type of IBD. In UC, signs of inflammation are present in continuous stretches of the large intestine (colon). In most cases, it involves the rectum (the last segment of the colon), which ends at the anus, where solid waste leaves the body. The most prominent locations of UC include the rectum and connecting part of the colon (proctitis), the left-sided colon, and the entire colon (pancolitis).

In contrast, CD can affect any part of the GI tract from the mouth to the anus, although the rectum and anus are often spared. Unlike UC, the inflammation in CD is not continuous and can sometimes affect patches of the GI tract while leaving other parts unaffected (called skip lesions). The 3 most prominent locations of CD are where the small intestine connects to the large intestine (ileocolonic), the last segment of the small intestine (ileal), and the colon.

Once established, intestinal inflammation tends to stay in the same place in IBD; however, in some cases can spread to other areas in the GI tract. (Source, Source)

Inflammation Differences

The layer of the GI tract affected, and the degree of inflammation present, differs between UC and CD. Inflammation in UC occurs in the superficial layers of affected areas, called the mucosal and submucosal layers. When affected areas are visualized with endoscopy, changes to the intestinal lining appear as unevenness in the mucosal layer, easily irritated and bleeding tissue, fluid accumulation, and pockets of immune cells within the lining’s crevices.

The inflammation in CD usually extends through the entire wall of the affected section of the GI tract. Additionally, in CD bleeding ulcers can be common, as well as tissue scarring and the presence of fistulas, or abnormal tunnels between parts of the body that shouldn’t be connected. (Source)

a person sitting down holding their knees to chest


Due to chronic blood loss from inflammation and frequent bloody stools, anemia is common in UC patients. Loss of appetite related to abdominal pain can also be common, leading to weight loss and malnutrition. Toxic megacolon is the swelling and lack of proper functioning of the colon, which can lead to toxin build-up in the body and be potentially life-threatening. It is rare, but can occur in either UC or CD. Toxic megacolon is more of a risk in UC because the colon is more likely to be affected. (Source)

Surgical removal of the colon, or colectomy, can be a life-saving procedure in the case of severe complications such as uncontrollable bleeding, megacolon, or cancer. The likelihood of undergoing colectomy increases over time, with about 10% of those with UC receiving colectomies 10 years after diagnosis. Colectomy rates are slowly falling as more effective medical treatments, such as biologics, are introduced. (Source, Source)

Complications of CD also include weight loss and malnutrition. The development of fistulas, bowel obstruction caused by scar tissue narrowing the intestines (strictures), and collections of pus (abscesses) in the GI tract is more common in CD. These complications increase the chances of infection or the need for surgery to remove affected areas. Short bowel syndrome, a condition that impairs absorption of nutrients, is a risk of multiple surgeries in which damaged parts of the small intestine are removed. (Source, Source)

Complications of IBD are also possible due to side effects of medications. It can be essential to balance the risks of medications with their benefits and consider additional approaches to supporting your health.

Use of Biomarkers in Inflammatory Bowel Disease

Due to the invasive nature and cost of colonoscopies, the use and relevance of laboratory tests for biomarkers of inflammation in the management of IBD has increased. C-reactive protein (CRP) and fecal calprotectin (FCP) are the markers most used to monitor treatment efficacy and inflammation status in IBD. While both markers have potential use in IBD management, CRP is more useful in CD, and FCP is more sensitive to inflammation in UC. These lab tests have limitations and are not stand-alone diagnostic tools, but can be used along with imaging to guide treatment. (Source)

Microbial Differences

Growing research connects gut bacteria to human health and disease. Not only are specific strains of bacteria beneficial (or harmful) for health, the balance between the different microbiota also plays a role. Gut microbiota balance is influenced by diet, medications, and stress. When out of balance, your immune system may be triggered to provoke an inflammatory response.

Specific differences in the gut microbiota between those with IBD and those without IBD are coming to light. Among several microbial differences, Mycobacterium avium paratuberculosis and Escherichia coli are increased in the colon in those with CD, and Clostridium difficile is elevated in both UC and CD. These bacteria are harmful to health when out of balance.

Additionally, Faecalibacterium prausnitizii, an anti-inflammatory bacterium, is decreased in those with CD. Ruminococcaceae, a bacteria class that helps us make bile acids, are deficient in UC patients who have had colectomies. Bile acids help maintain gut bacteria balance and aid in the digestion of dietary fat. (Source, Source)

a bowl of vegetables and a glass jar of juice

Additional IBD Resources

For more resources and support for IBD, look into the following groups and organizations:

American College of Gastroenterology

Crohn’s and Colitis Community

Crohn’s and Colitis Foundation

Institute for Functional Medicine

The Bottom Line on Crohn’s vs. UC

The symptoms of ulcerative colitis and Crohn’s disease tend to overlap, although they usually come on more gradually with UC and more suddenly with Crohn’s. Visualizing the GI tract with endoscopy can uncover distinct patterns and features of inflammation that distinguish the two conditions. There are also differences in the presence of inflammatory biomarkers, the makeup of the gut microbiome, and possible complications. Different immune-system targeted medications are available for IBD treatment, and are chosen based on your health and level of disease activity.

While nutrition is a potential risk factor for IBD, it is also a powerful support for managing your condition including mucosal healing, a sign of deep remission. Nutritional therapists at WellTheory can meet you where you’re at and support you with a comprehensive and inclusive approach to managing your health. Learn more about our membership options for individualized support.

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