Crohn's Disease or Ulcerative Colitis: How Do They Differ?

Crohn's disease vs ulcerative colitis comes down mainly to where and how deep the inflammation sits. Ulcerative colitis affects the inner lining of the colon and rectum in a continuous stretch. Crohn's disease can affect any part of the digestive tract, often in patches, and can involve the full thickness of the bowel wall. This article compares symptoms, complications, testing and treatment, and lists the signs that need urgent care.

Crohn's disease vs ulcerative colitis: the short version

Both conditions are types of inflammatory bowel disease (IBD). In both, the immune system appears to drive long-term inflammation in the digestive tract, and both tend to come in flares and quieter periods. Neither is the same as irritable bowel syndrome, which does not cause visible inflammation. If that is your question, see our article on irritable bowel syndrome.

The differences that matter most to patients and doctors are location, depth, pattern and complications.

This is a general pattern. Some people have features of both, and doctors sometimes cannot assign one label at first. The review Ulcerative colitis and Crohn's disease: similarities and distinctions in PubMed Central describes the overlap as well as the differences.

Where the inflammation sits and why it matters

In ulcerative colitis, inflammation begins in the rectum in most cases and can spread upward through part or all of the colon. It stays in the colon. MedlinePlus describes ulcerative colitis as causing sores and inflammation in the lining of the large intestine.

In Crohn's disease, inflammation can appear anywhere along the digestive tract. MedlinePlus notes that it often affects the small intestine and the beginning of the large intestine, and that it can reach deeper layers of the bowel wall. Because the small intestine absorbs nutrients, Crohn's disease may be associated with weight loss, anemia and low levels of nutrients such as vitamin D. Ulcerative colitis can also cause anemia, usually through blood loss.

Location also shapes symptoms. Colon-only disease tends to produce urgency and frequent stools. Disease in the small intestine may cause cramping pain after eating and weight loss with less obvious diarrhea.

Symptoms: how each condition can feel

Ulcerative colitis symptoms

• Diarrhea that often contains blood or mucus
• Sudden, urgent need to have a bowel movement
• Rectal pain or a feeling of needing to go when little comes out
• Cramping, usually in the lower belly
• Fatigue and, in more active disease, weight loss

Crohn's disease symptoms

• Abdominal pain, often in the lower right side but sometimes elsewhere
• Diarrhea, which may or may not contain visible blood
• Weight loss and poor appetite
• Fatigue, and sometimes low-grade fever
• Mouth sores, or pain, swelling or drainage near the anus

Visible blood in the stool can be a clue pointing toward colitis, but it does not settle the question. Hemorrhoids are a very common reason for bright red blood on toilet paper, and MedlinePlus lists their typical features. Blood that is mixed into loose stool, or that comes with diarrhea, pain or weight loss, deserves evaluation rather than self-diagnosis. For people younger than 50, our article on colorectal cancer in people under 50 explains which bowel symptoms deserve a colonoscopy.

Complications that differ between the two

Complications more associated with Crohn's disease

Because Crohn's inflammation can go through the whole bowel wall, it may lead to scarring and narrowing called strictures. A stricture can partly block the intestine, causing cramping pain, bloating and vomiting. Deep inflammation can also create abnormal tunnels called fistulas, which can connect the bowel to the skin around the anus, the bladder, the vagina or other loops of bowel. MedlinePlus explains fistulas in more detail. Collections of infection called abscesses can also form.

Complications more associated with ulcerative colitis

Severe ulcerative colitis can cause heavy bleeding and, in some cases, a dangerous swelling of the colon sometimes called toxic megacolon, with a swollen belly, fever and a fast heartbeat. Having colitis for many years is associated with a higher risk of colorectal cancer. Gastroenterology society guidelines recommend surveillance colonoscopy starting several years after diagnosis in long-standing colitis, and your gastroenterologist sets the timing for you. See MedlinePlus on colorectal cancer for general background.

Problems outside the gut

Both conditions can affect other parts of the body. Joint pain and inflammatory arthritis can occur, as can eye inflammation, skin problems and mouth sores. Inflammation of the bile ducts called primary sclerosing cholangitis is more often linked with colitis than with Crohn's disease. People with IBD may also have a higher chance of blood clots during flares. Tell your clinician about any of these so they can decide whether they are related to your bowel disease.

How doctors tell them apart

No single test separates the two in every person. Clinicians combine your history, a physical examination and several tests.

• Blood and stool tests. Blood counts and markers of inflammation can point toward IBD. Stool tests can look for infection, which can mimic a flare, and for markers of bowel inflammation.
• Colonoscopy with biopsies. A camera examines the colon and the end of the small intestine, and small tissue samples are studied under a microscope. A continuous pattern starting at the rectum fits ulcerative colitis, while patchy areas fit Crohn's disease. Some biopsy findings, such as granulomas, are seen in some people with Crohn's disease but not in everyone.
• Imaging. CT or MRI of the small bowel can show strictures, fistulas and inflammation beyond the reach of the colonoscope. Capsule endoscopy or upper endoscopy is sometimes added.

Sometimes the picture is unclear, particularly early on, and a doctor may use a working label such as indeterminate colitis and revisit the diagnosis over time. Researchers are also studying blood inflammation signatures that may distinguish the two, but these are not a substitute for standard evaluation.

Other conditions can look similar, including infections, diverticulitis (see MedlinePlus on diverticulosis and diverticulitis), celiac disease and microscopic colitis. Our article on celiac disease covers that overlap.

Treatment: what is shared and what differs

The goals are similar for both: calm active inflammation, keep it quiet, prevent complications and support nutrition. The right plan depends on the diagnosis, the location, how severe it is and your other health conditions. Your gastroenterologist decides this with you.

• Aminosalicylates such as mesalamine. These are used more often in ulcerative colitis than in Crohn's disease.
• Corticosteroids. These may be used for short periods to bring a flare under control. They are generally not meant for long-term use because of side effects.
• Immunomodulators. Medicines that dampen immune activity are used in both conditions and require blood test monitoring.
• Biologic medicines. These include infliximab and vedolizumab. A PubMed Central systematic review and meta-analysis comparing infliximab and vedolizumab looked at how the two compare for efficacy and safety in IBD. Outcomes vary from person to person.
• Newer oral medicines such as JAK inhibitors (for example tofacitinib) are also used in some situations. Their labels carry boxed warnings that include serious infections, death, cancer, major cardiovascular events and blood clots, and they are generally considered after other treatments. Ask your prescriber about these risks, and report any clot symptoms promptly.
• Surgery. In ulcerative colitis, removing the colon removes the diseased colon, though some people develop pouch inflammation and symptoms outside the bowel can continue. In Crohn's disease, surgery removes damaged segments or treats strictures and fistulas, but inflammation can return elsewhere.

Safety note on medicines. Biologics, immunomodulators, steroids and JAK inhibitors work by changing immune activity. Their labels carry cautions that include a higher risk of serious infections, and some carry additional warnings. Read the medication guide and ask your prescriber or pharmacist about vaccines, infection screening and which warning signs to report. Do not change the dose or timing of a prescription, and do not skip recommended blood tests or monitoring, without talking to your prescriber.

Over-the-counter medicines deserve the same care. Anti-inflammatory pain relievers such as ibuprofen, naproxen and aspirin can be associated with flares in some people with IBD, so avoid them unless your clinician has approved them. Antidiarrheal medicines such as loperamide can be risky during a severe flare with bloody diarrhea, fever or a swollen belly, because they may contribute to toxic megacolon. Use them only if a clinician says so.

Everyday factors: smoking, food and long-term care

Smoking is associated with a worse course in Crohn's disease, and quitting is often recommended by clinicians. The relationship with ulcerative colitis is more complicated, and smoking is not a recommended treatment. Diet is not established as the cause or the cure of either disease. Foods that worsen symptoms differ from person to person, and during a stricture, clinicians may suggest lower-fiber choices. A dietitian experienced with IBD can help you avoid unnecessary restriction that leads to weight loss.

Long-term care often includes periodic blood tests for anemia and nutrient levels, bone health review if you have used steroids repeatedly, and vaccine review before starting immune-suppressing medicines. Monitoring differs by medicine: immunomodulators usually involve regular blood tests, and biologics and JAK inhibitors usually involve infection screening before and during treatment. Ask your clinician about checking vitamin D, iron and vitamin B12 in your situation.

Pregnancy, fertility and childhood onset need individual planning. IBD can begin in children and teenagers, and growth and puberty are part of what a pediatric gastroenterologist follows. If you are pregnant or hoping to become pregnant, tell your gastroenterologist early, because some IBD medicines have pregnancy cautions on their labels and disease activity itself can matter. Do not stop or change a medicine on your own.

When symptoms need care

Certain features of either condition call for emergency evaluation: a rigid, very painful belly with fever, a swollen belly with vomiting and no passing of gas or stool, heavy bleeding with lightheadedness, and signs of a blood clot. Fever with severe or worsening belly pain while taking steroids, immunomodulators or biologics also belongs here, because these medicines can blunt fever and belly tenderness and mask abscess, perforation or serious infection. These are listed in the emergency box below. Other changes, such as new blood in the stool, ongoing diarrhea or weight loss, deserve a prompt visit with a clinician, even if they come and go. A clinician can sort out whether it is IBD, an infection, hemorrhoids or something else.

When to Seek Medical Care