Colitis simply means inflammation of the colon, but the term covers several distinct conditions with different causes, patterns, and treatments. The three types most people encounter are ulcerative colitis, Crohn’s colitis, and microscopic colitis. These are the chronic, immune-related forms that require long-term management. Two other common types, infectious colitis and ischemic colitis, tend to come on suddenly and often resolve once the underlying trigger is treated. Here’s what sets each one apart.
Ulcerative Colitis
Ulcerative colitis (UC) is a chronic inflammatory bowel disease that affects only the innermost lining of the colon. It never reaches through the deeper layers of the intestinal wall. The inflammation always starts in the rectum and spreads upward in one continuous stretch, leaving no healthy tissue along its path. This continuous pattern is one of the key features doctors look for when distinguishing UC from other forms of colitis.
Symptoms typically include bloody diarrhea, urgent bowel movements, abdominal cramping, and fatigue. During a colonoscopy, the colon lining appears granular and fragile, with visible ulcers, erosions, or small polyp-like growths. A diagnosis requires both these visual signs and microscopic evidence of chronic inflammation on biopsy, usually observed over at least six months.
UC is one of the two main inflammatory bowel diseases, and its prevalence is rising. Compounded rates of inflammatory bowel disease in North America, Europe, and Australasia are projected to reach 1 in 100 people by the end of this decade, with accelerating rates in Asia, Africa, and Latin America as well. Treatment starts with anti-inflammatory medications designed to calm the immune response in the colon lining. For mild to moderate disease, these medications can often bring symptoms under control and keep them in remission. More severe cases may need stronger immune-suppressing therapies or, in some situations, surgery to remove the affected portion of the colon.
Crohn’s Colitis
Crohn’s disease can strike anywhere in the digestive tract, from the mouth to the anus. When it specifically involves the colon, it’s called Crohn’s colitis. It differs from ulcerative colitis in two important ways: the inflammation is transmural, meaning it goes through the full thickness of the bowel wall, and it appears in “skip lesions,” distinct patches of inflamed tissue with healthy stretches in between.
That full-thickness inflammation has real consequences. It can lead to rigid thickening of the bowel wall, deep fissures, and abnormal tunnels (fistulas) that connect the intestine to other organs or the skin surface. Abscesses can form around these tunnels. These complications don’t happen with ulcerative colitis because UC stays in the superficial lining.
Symptoms overlap with UC and include diarrhea, abdominal pain, fatigue, and weight loss. Bloody stool is possible but less consistent than in UC. The skip-lesion pattern is often visible during colonoscopy, with clearly inflamed segments next to normal-looking tissue. Treatment follows a similar ladder to UC: anti-inflammatory drugs first, then immune-suppressing therapies for moderate to severe disease. Corticosteroids may be used short-term to get flares under control but aren’t meant for long-term use.
Microscopic Colitis
Microscopic colitis gets its name from the fact that the colon looks completely normal during a colonoscopy. The inflammation only shows up when a tissue sample is examined under a microscope. This makes it easy to miss if biopsies aren’t taken.
There are two subtypes. In collagenous colitis, a thick band of collagen protein builds up in the colon tissue. In lymphocytic colitis, white blood cells called lymphocytes accumulate in the lining in abnormally high numbers. Both subtypes cause the same hallmark symptom: chronic, watery diarrhea without blood. That lack of visible blood is a useful clue that distinguishes microscopic colitis from UC and Crohn’s colitis.
Microscopic colitis is more common in older adults, particularly women, and is sometimes linked to certain medications. Treatment is generally effective, and many people achieve remission with medication that targets inflammation locally in the colon.
Infectious and Ischemic Colitis
Beyond the three chronic types, two acute forms of colitis are worth knowing about because they’re common and can mimic the symptoms of inflammatory bowel disease.
Infectious colitis is the most frequent cause of colon inflammation overall, especially in children. It’s caused by bacteria, viruses, or parasites. Common bacterial culprits include E. coli, Salmonella, Shigella, and Campylobacter. The parasitic infection most widespread globally is caused by Entamoeba histolytica, typically transmitted through contaminated water or poor sanitation. Viral infections, including adenovirus, can cause severe colitis in people with weakened immune systems. Symptoms include diarrhea (often bloody), abdominal pain, and fever. Most cases resolve with treatment of the underlying infection, though some require supportive care to prevent dehydration.
Ischemic colitis occurs when blood flow to part of the colon drops enough that the tissue doesn’t get sufficient oxygen. The cells become damaged and swollen. Risk factors include atherosclerosis (fatty deposits narrowing arteries), low blood pressure, dehydration, heart failure, diabetes, and heavy exercise like marathon running. Certain medications and recreational drugs, including cocaine and methamphetamines, can also trigger it. Symptoms come on suddenly with abdominal pain and rectal bleeding. Most cases are mild and resolve on their own as blood flow returns, but severe episodes can damage the colon permanently.
How Doctors Tell Them Apart
The diagnostic process usually starts with blood tests and stool samples to rule out infection. If symptoms persist or suggest a chronic condition, a colonoscopy is the next step. During the procedure, the doctor looks at the pattern and distribution of inflammation. Continuous inflammation starting at the rectum points toward UC. Patchy inflammation with healthy gaps suggests Crohn’s colitis. A normal-looking colon with chronic watery diarrhea raises suspicion for microscopic colitis, but only a biopsy can confirm it.
Tissue samples are taken during colonoscopy regardless of what the colon looks like. Under the microscope, each type has a distinct signature: UC shows chronic inflammation confined to the surface lining, Crohn’s shows full-thickness involvement, and microscopic colitis shows either excess collagen or excess lymphocytes. Stool cultures that come back negative for infection further support an inflammatory bowel disease diagnosis, though doctors typically want to see evidence of chronic changes over time before making it official.
Treatment Differences at a Glance
Medication is the first line of treatment for all three chronic types, but the specific approach varies. For mild to moderate UC, anti-inflammatory drugs that target the colon lining are often enough to control symptoms and maintain remission. Crohn’s colitis, because of its deeper and more unpredictable inflammation, frequently requires stronger immune-suppressing therapies earlier in the course of disease. Newer targeted therapies are now available for moderate to severe cases of both UC and Crohn’s.
Corticosteroids play a role in managing flares across both conditions but are only meant for short-term use due to side effects with prolonged exposure. If initial medications fail, doctors step up to immunomodulators or biologic therapies that block specific parts of the immune response driving the inflammation.
Microscopic colitis typically responds well to a single anti-inflammatory medication, and many people experience significant improvement within weeks. Infectious colitis is treated by targeting the specific pathogen, whether bacterial, viral, or parasitic. Ischemic colitis usually requires supportive care: IV fluids, bowel rest, and monitoring while blood flow recovers.