Colitis

Colitis means inflammation of the colon, also called the large intestine. The colon absorbs water and stores stool before a bowel movement. When its lining becomes inflamed, it may cause diarrhea, abdominal pain, urgency, or blood in the stool.

Colitis is not one specific disease. It is a general term for several conditions with different causes and treatments. Important types include:

• Ulcerative colitis, a long-term inflammatory bowel disease in which the immune system contributes to ongoing inflammation
• Infectious colitis, caused by bacteria, viruses, or parasites
• Microscopic colitis, which causes long-lasting watery diarrhea and is diagnosed by examining colon tissue under a microscope
• Ischemic colitis, caused by reduced blood flow to part of the colon
• Medicine-related colitis, which may occur with certain medicines or cancer treatments
• Radiation colitis, which can develop after radiation treatment involving the abdomen or pelvis

Some cases begin suddenly and improve after the underlying cause is treated. Others are chronic, meaning they continue for a long time or return in periods called flares. Finding the cause matters because treatment for one type of colitis may not help another. For example, antibiotics like amoxicillin or doxycycline may treat a specific bacterial infection but are not routine treatment for ulcerative colitis.

Symptoms depend on the cause, the part of the colon affected, and the severity of inflammation. Common symptoms include:

• Diarrhea, which may be watery or bloody
• Abdominal pain or cramping
• A sudden or frequent need to have a bowel movement
• A feeling that the bowel has not emptied fully
• Mucus in the stool
• Rectal bleeding
• Fever
• Nausea or reduced appetite
• Fatigue
• Unintended weight loss

Ulcerative colitis often causes bloody diarrhea, urgency, and cramping. Microscopic colitis usually causes frequent watery diarrhea without visible blood. Infectious colitis may cause fever, vomiting, or symptoms that begin after travel, contaminated food, an illness outbreak, or antibiotic use.

Ischemic colitis often causes sudden abdominal pain, followed by an urgent bowel movement or blood in the stool. It is more common in older adults, but it can occur in other people when blood flow to the colon is disrupted.

When to seek urgent or emergency care

Contact a healthcare professional promptly for new blood in the stool, diarrhea that continues for more than a few days, repeated nighttime diarrhea, unexplained weight loss, or symptoms that return after improving. People with a known form of colitis should also report a clear increase in bowel movements, bleeding, pain, or fever.

Seek emergency care for:

• Severe or rapidly worsening abdominal pain
• Heavy rectal bleeding, passing large blood clots, or black, tar-like stool
• Fainting, confusion, marked weakness, or trouble staying awake
• A swollen or rigid abdomen
• Inability to keep fluids down
• Signs of severe dehydration, such as very little urine, severe dizziness, or a rapid heartbeat

These symptoms do not confirm a particular diagnosis, but they can occur with serious bleeding, severe infection, reduced blood flow, or dangerous colon swelling.

The causes of colitis vary widely.

Ulcerative colitis involves an abnormal immune response that damages the inner lining of the colon. Genes, the immune system, and environmental factors appear to interact. It is not caused by stress or a particular food, although stress and some foods may make symptoms feel worse during a flare. A family history of inflammatory bowel disease can increase risk.

Infectious colitis can result from foodborne or waterborne germs. It may also spread from another person. Recent antibiotic use or a healthcare stay can increase the risk of Clostridioides difficile, often called C. diff. This bacterium can multiply when antibiotics disrupt the usual balance of bacteria in the colon.

Microscopic colitis has no single known cause. Immune activity, genetics, smoking, and some medicines may contribute. Medicines associated with microscopic colitis include certain pain relievers, acid-suppressing drugs, and antidepressants like sertraline or fluoxetine, but an association does not prove that a medicine caused an individual case. Do not stop a prescribed medicine without discussing it with a clinician.

Ischemic colitis develops when the colon temporarily receives too little blood. Risk may be higher with older age, blood vessel disease, heart rhythm problems, low blood pressure, dehydration, blood-clotting disorders, or surgery involving major blood vessels. Some medicines and drugs can narrow blood vessels or affect blood flow.

Other causes include radiation treatment, reduced immune defenses, and immune-based cancer treatments called checkpoint inhibitors. Inflammation can also occur near an intestinal pouch or after certain operations.

Diagnosis starts with a medical history and physical examination. A clinician may ask when symptoms began, how often bowel movements occur, whether stool contains blood, and whether symptoms happen at night. Travel, food exposures, recent antibiotics, medicines, family history, and prior bowel conditions are also relevant.

Testing may include:

• Blood tests to look for anemia, inflammation, infection, dehydration, or changes in liver and kidney function
• Stool tests to check for bacteria, parasites, C. diff, or signs of intestinal inflammation
• Colonoscopy, in which a flexible camera examines the colon
• Flexible sigmoidoscopy, which examines the rectum and lower colon
• Biopsy, the removal of tiny tissue samples during an endoscopic procedure
• Imaging, such as a CT scan, when severe inflammation, reduced blood flow, a complication, or another cause of pain is suspected

A biopsy is especially important for microscopic colitis because the colon may look normal during colonoscopy. The diagnosis is made by finding characteristic inflammation in tissue under a microscope.

Stool testing can help distinguish infection from inflammatory bowel disease, but no single test answers every question. A stool marker called fecal calprotectin can show that intestinal inflammation may be present. It cannot, by itself, identify the exact cause.

Treatment depends on the type and severity of colitis. The goals may include replacing lost fluids, treating an infection or blood-flow problem, controlling inflammation, easing symptoms, and preventing complications.

For mild short-term illness, supportive care may include adequate fluids and food as tolerated. Oral rehydration solutions can replace water and salts lost through diarrhea. Restrictive diets are not a universal treatment for colitis. During active symptoms, some people temporarily tolerate smaller meals and lower-fiber foods better, but nutritional needs differ.

Do not use an anti-diarrheal medicine without professional advice when diarrhea is bloody, fever is present, or severe colitis is possible. Slowing the bowel can be unsafe in some infections or in severe inflammation.

Treatment for specific forms of colitis

Infectious colitis may improve with hydration alone, depending on the germ. Antibiotics are used for selected bacterial infections, not for every case of diarrhea. Treatment for C. diff uses specific antibiotics chosen for that infection. A clinician may also review whether another antibiotic can be stopped safely.

Ulcerative colitis treatment is based on how much of the colon is affected and how active the inflammation is. Medicines may include aminosalicylates, corticosteroids like prednisone or hydrocortisone for short-term control of a flare, immune-modifying medicines, biologic therapies, or targeted oral medicines. Corticosteroids are generally used to bring inflammation under control rather than as long-term maintenance treatment.

Medicines commonly used for ulcerative colitis include adalimumab. Which one suits you, if any, is a decision for you and your doctor.

Surgery to remove the colon can cure the colon inflammation caused by ulcerative colitis. It may be considered when medicines do not control the disease, complications develop, or precancerous or cancerous changes are found. Surgery changes how stool leaves the body, so detailed planning with an experienced surgical team is important.

Microscopic colitis management may include reviewing possible medicine triggers, stopping smoking, and using an anti-inflammatory medicine that acts mainly in the intestine. Persistent diarrhea may require additional evaluation for related problems, such as bile acid diarrhea or celiac disease.

Ischemic colitis may be managed with bowel rest, intravenous fluids, and treatment of the problem affecting circulation. Antibiotics may be used in some cases. Surgery can be necessary if part of the colon is badly damaged, develops a hole, or does not heal.

Medicine-related or radiation-related colitis requires care tailored to the cause. When immune-based cancer treatment is involved, the oncology team should be contacted promptly because treatment may need to be paused and inflammation treated.

Many people recover without lasting damage, but complications depend on the cause and severity.

Significant diarrhea or bleeding can lead to dehydration, low blood pressure, iron deficiency, or anemia. Severe inflammation can occasionally cause a hole in the colon, widespread infection, or toxic megacolon. Toxic megacolon is a dangerous widening of the colon that can occur with severe inflammatory or infectious colitis.

Ischemic colitis can cause scarring that narrows the colon. If tissue loses its blood supply for too long, part of the bowel can die and require surgery.

Long-standing ulcerative colitis affecting much of the colon increases colorectal cancer risk. Risk is influenced by how long the disease has been present, how much colon is involved, the degree of inflammation, family history, and certain related liver and bile duct conditions. This is why some people need scheduled surveillance colonoscopies even when symptoms are controlled.

Chronic symptoms may also affect sleep, work, nutrition, and emotional well-being. These effects are valid parts of the illness and can be discussed during follow-up visits.

Follow-up should focus on both symptoms and control of inflammation. Feeling better does not always mean the colon has fully healed.

A clinician may monitor bowel frequency, bleeding, weight, blood counts, iron levels, inflammatory markers, or fecal calprotectin. Repeat colonoscopy may be recommended to check healing, clarify a diagnosis, remove polyps, or watch for precancerous changes in people with long-standing ulcerative colitis.

People taking immune-modifying treatment may need laboratory monitoring and infection-prevention planning. Vaccination needs should be reviewed before or during treatment because some therapies reduce immune defenses. Any decision to change or stop treatment should be made with the prescribing clinician.

Routine follow-up is appropriate for stable symptoms, medication monitoring, nutrition concerns, or planning surveillance tests. New fever, increasing bleeding, worsening pain, frequent vomiting, or signs of dehydration deserve prompt contact with a healthcare professional. Severe pain, heavy bleeding, fainting, confusion, or a swollen rigid abdomen require emergency evaluation.