Colitis is inflammation of the colon, and its hallmark symptoms are diarrhea, abdominal pain, and an urgent need to use the bathroom. Beyond those core symptoms, the specific pattern varies depending on the type of colitis you have. Some forms cause bloody stool, others produce watery diarrhea without blood, and still others strike suddenly with cramping on one side of the abdomen.
Core Symptoms Across All Types
Regardless of the cause, most people with colitis experience some combination of these symptoms:
- Diarrhea, which may be watery or contain blood and mucus
- Abdominal pain or cramping, often in the lower belly
- Urgency, a sudden, hard-to-delay need to reach a toilet
- Tenesmus, the feeling that you still need to go even after a bowel movement
- Fatigue that goes beyond normal tiredness
- Fever, particularly during flares or infections
How these symptoms combine and how quickly they appear are important clues to which type of colitis is involved.
Ulcerative Colitis Symptoms
Ulcerative colitis (UC) is a chronic inflammatory bowel disease that affects the inner lining of the colon and rectum. Its defining symptom is bloody diarrhea, often mixed with mucus. Abdominal cramping tends to worsen before bowel movements and ease slightly afterward. Because UC almost always involves the rectum, urgency and tenesmus are particularly common.
Symptoms typically develop gradually over weeks rather than appearing overnight. Stool frequency is one of the key markers clinicians use to gauge severity: mild disease may mean four or fewer loose stools a day, while severe flares can push that number well above six, accompanied by significant bleeding and fever. UC follows a relapsing-remitting pattern, meaning you can have stretches of feeling normal between flares that last weeks or months.
Population-based data show UC prevalence varies widely by region but is rising. A 2024 study from Canterbury, New Zealand, recorded 264 cases per 100,000 people, nearly double the rate found in the same population in 2005. Similar trends appear across high-income countries, with some populations (like the Faroe Islands) reaching UC rates above 900 per 100,000.
Infectious Colitis: A Different Pattern
When colitis is caused by a bacterial, viral, or parasitic infection, the onset is usually sudden. Fever tends to arrive early, diarrhea can exceed six or more watery or bloody bowel movements a day, and the whole episode often resolves within days to a couple of weeks as the infection clears. In a prospective study comparing acute infectious colitis with IBD, sudden onset and early fever were the strongest distinguishing features of infection, while IBD patients had a more gradual buildup and fewer daily bowel movements early on.
Food poisoning, traveler’s diarrhea, and C. diff infections (often triggered by antibiotic use) are common culprits. The key practical difference: infectious colitis is usually self-limiting, while inflammatory bowel disease persists and requires ongoing management.
Microscopic Colitis: No Visible Inflammation
Microscopic colitis is one of the more frustrating forms to identify because the colon looks completely normal during a colonoscopy. The inflammation only shows up under a microscope, which is how it gets its name. It causes chronic, watery, nonbloody diarrhea. The absence of blood is an important distinction from ulcerative colitis.
This type is most common in older adults and can easily be mistaken for irritable bowel syndrome (IBS) because the symptoms overlap and standard imaging looks unremarkable. The diarrhea is secretory, meaning the colon is actively pushing fluid into the stool rather than simply failing to absorb it. Episodes can persist for months and significantly disrupt daily life, even though the condition is not associated with the same cancer risk as UC.
Ischemic Colitis: Reduced Blood Flow
Ischemic colitis happens when blood flow to part of the colon drops low enough to damage the tissue. It most commonly affects adults over 60, particularly those with atherosclerosis, heart failure, or low blood pressure. Pain, tenderness, or cramping in the belly, usually on the left side, is the classic first symptom. Bright red or maroon blood in the stool often follows shortly after, sometimes passing on its own without any stool at all.
Right-sided ischemic colitis is less common but more dangerous. People with right-sided symptoms tend to have more underlying cardiovascular conditions and face a higher risk of needing surgery. Risk factors include dehydration, recent surgery on the heart or blood vessels, blood-clotting disorders, and use of stimulant drugs like cocaine or methamphetamines.
Symptoms Beyond the Gut
Chronic inflammatory colitis, particularly UC and Crohn’s disease, can produce symptoms in parts of the body that seem unrelated to the colon. These are called extraintestinal manifestations, and they have been reported in nearly every organ system.
Joint problems are the most common. Inflammatory arthritis can affect the knees, ankles, wrists, or spine, causing pain, swelling, and stiffness that may flare alongside gut symptoms or independently. Skin manifestations appear in roughly 2 to 34 percent of people with inflammatory bowel disease. The two most frequent are erythema nodosum (tender, deep nodules typically on the shins) and pyoderma gangrenosum (a rapidly expanding skin ulcer with a purple border).
Eye inflammation, including uveitis and episcleritis, can cause redness, pain, and blurred vision. Mouth ulcers are also common. These symptoms tend to be more frequent in IBD than in infectious colitis, so their presence alongside chronic diarrhea is an important signal that something more than an infection may be going on.
How Colitis Affects Children Differently
Children with colitis experience the same gut symptoms as adults, but the consequences extend further. Growth failure is one of the most significant complications of pediatric inflammatory bowel disease. It can show up before the classic digestive symptoms do, meaning a child may fall behind on growth charts before anyone suspects colitis.
The causes are layered: abdominal pain reduces appetite, inflamed intestinal walls absorb fewer nutrients, and the chronic inflammatory state itself interferes with how the body responds to growth hormone. Children with Crohn’s disease affecting the colon are especially vulnerable, with upper GI symptoms like nausea and poor appetite reported in the majority of cases in some studies. When colitis begins before puberty, the risk of not reaching expected adult height increases, making early diagnosis and nutritional support especially important.
Testing for Colitis
If your symptoms suggest colitis, one of the simplest initial tests is a fecal calprotectin test. This is a stool sample that measures a protein released by white blood cells during inflammation. Normal levels generally suggest your symptoms are not caused by colitis and point more toward IBS. Very high levels strongly suggest inflammatory bowel disease. Moderately elevated levels can indicate a range of conditions, from severe infections to diverticulitis to microscopic colitis. The test is useful because it can help determine whether you need a colonoscopy without jumping straight to that procedure.
Colonoscopy remains the definitive diagnostic tool. It allows direct visualization of the colon lining and, critically, tissue sampling. This is the only way to diagnose microscopic colitis, where the colon appears normal to the naked eye but shows characteristic changes under a microscope.
Serious Warning Signs
Most colitis episodes are manageable, but certain symptoms signal complications that need immediate attention. Toxic megacolon occurs when severe inflammation paralyzes the colon muscles, causing the colon to swell dangerously with trapped gas and stool. Signs include a rapidly distending abdomen, high fever, rapid heart rate, and worsening pain. Perforation, where inflammation or an ulcer wears a hole through the colon wall, can allow bacteria to leak into the abdominal cavity, causing life-threatening infection.
Seek emergency care for abdominal pain that keeps getting worse rather than cycling with flares, large amounts of blood in your stool, high fever with abdominal distension, or diarrhea so severe you cannot stay hydrated. Persistent bloody diarrhea that lasts more than a few days also warrants prompt evaluation, even if you feel otherwise stable.