Ulcerative colitis is inflammation of the colon and rectum that causes bloody diarrhea and abdominal pain

Ulcerative colitis is a condition where the lining of your colon (the large intestine) and rectum becomes inflamed and develops small sores called ulcers. These ulcers bleed and produce mucus, which is why the most common symptom is diarrhea mixed with blood. The inflammation starts in the rectum and spreads upward into the colon, but it only affects the innermost lining—not the deeper layers of the bowel wall.

This is different from Crohn's disease, another inflammatory bowel condition, because Crohn's can affect any part of the digestive tract from mouth to anus and can involve all layers of the bowel. Ulcerative colitis is limited to the colon and rectum and stays in the surface layer.

The condition is chronic, meaning it lasts a long time. Some people have long stretches without symptoms, while others deal with flares—periods when symptoms get worse—regularly. It is not contagious and is not caused by stress, though stress can make symptoms worse.

Key Takeaways

  • Ulcerative colitis causes inflammation and ulcers in the colon and rectum, leading to bloody diarrhea, abdominal pain, and urgency to have bowel movements.
  • Doctors diagnose it using a colonoscopy, where they look directly at the colon and take small tissue samples to confirm inflammation.
  • Blood tests and stool tests help rule out infections and show whether inflammation is active.
  • Symptoms vary widely—some people have mild disease with few flares, while others have frequent severe symptoms.
  • Treatment focuses on reducing inflammation and managing symptoms, with options ranging from medications to surgery in severe cases.

What symptoms should make you see a doctor

The hallmark symptom is diarrhea that contains blood or mucus. You may also have abdominal cramping, pain in the lower left side of your belly, and a constant urge to have a bowel movement even when your bowel is empty. Some people lose weight without trying, feel tired, or run a fever during flares.

Symptoms can range from mild to severe. Mild disease might mean three to four loose stools a day with small amounts of blood. Severe disease can mean ten or more stools daily with heavy bleeding, severe cramping, and fever. The pattern is unpredictable—you might have no symptoms for months, then a flare lasting weeks or longer.

See a doctor if you have diarrhea lasting more than a few weeks, blood in your stool, or ongoing abdominal pain. These symptoms can have other causes, but they warrant investigation. If you have severe diarrhea, fever, and abdominal pain all at once, seek care the same day, as this can signal a serious flare.

How doctors diagnose ulcerative colitis

Your doctor will start by asking about your symptoms, how long they have lasted, and whether anyone in your family has inflammatory bowel disease. They will do a physical exam and order blood tests to look for signs of inflammation and anemia (low red blood cell count from bleeding).

The main diagnostic test is a colonoscopy. During this procedure, you receive sedation and the doctor inserts a thin, flexible tube with a camera into your rectum and guides it through your entire colon. They can see the inflamed areas and ulcers directly. The doctor also takes small tissue samples (a biopsy) from several spots in the colon. These samples are examined under a microscope to confirm the inflammation pattern is consistent with ulcerative colitis rather than another condition.

Your doctor may also order a stool test to rule out infections that can cause similar symptoms, and imaging tests like a CT scan if they suspect complications. Once diagnosed, you may have blood tests repeated during treatment to monitor how well medications are working.

What causes ulcerative colitis

The exact cause is not fully understood, but it involves both genetics and the immune system. If a close relative has ulcerative colitis or Crohn's disease, your risk is higher. However, most people with a family history never develop the condition, so genetics is not the whole story.

The leading theory is that in people with ulcerative colitis, the immune system mistakenly attacks the lining of the colon. Normally, the immune system protects against harmful bacteria and viruses. In ulcerative colitis, it treats the colon lining as a threat and causes inflammation. Why this happens is still being researched—factors under study include gut bacteria composition, intestinal barrier function, and environmental triggers.

Stress does not cause ulcerative colitis, but it can worsen flares in people who already have it. Diet does not cause it either, though certain foods may trigger symptoms in individual people.

How ulcerative colitis affects your body during a flare

During a flare, the inflamed areas of the colon bleed and produce excess mucus. Your colon becomes irritated and contracts more often, pushing stool through faster than normal. This is why you have frequent, urgent bowel movements and diarrhea. The bleeding can be visible in the stool or only detectable by a blood test.

The inflammation can also affect how your colon absorbs water and nutrients. Chronic diarrhea means you lose fluids and electrolytes (minerals like sodium and potassium), which can lead to dehydration and fatigue. If bleeding is heavy or ongoing, you can develop anemia.

Beyond the colon, ulcerative colitis can cause problems in other parts of the body. Some people develop joint pain, skin rashes, eye inflammation, or liver problems. These are called extraintestinal manifestations. They are less common than bowel symptoms but can be serious and may need separate treatment.

Treatment options and what to expect

Treatment aims to reduce inflammation, heal the ulcers, and manage symptoms so you can feel better and prevent flares. Most people start with medications. Aminosalicylates (like mesalamine) reduce inflammation and are often the first choice for mild to moderate disease. They come as pills, enemas, or suppositories depending on where in the colon the inflammation is.

If aminosalicylates do not work well enough, doctors move to corticosteroids (like prednisone) to calm the immune system quickly during flares. These are powerful but are not meant for long-term use because of side effects. Immunosuppressants (like azathioprine) and biologic medications (like infliximab or vedolizumab) work by targeting specific parts of the immune system. These are used when other medications have not controlled symptoms.

Most people manage ulcerative colitis with medication and do not need surgery. However, if medications fail, the colon is severely damaged, or complications develop, surgery to remove the colon and rectum is an option. This is curative because ulcerative colitis only affects the colon—removing it eliminates the disease. After surgery, bowel function is restored through a pouch made from the small intestine.

Living with ulcerative colitis long-term

Many people with ulcerative colitis have long periods of remission—months or years with no symptoms. Others have frequent flares. The course is unpredictable, and what works for one person may not work for another, so treatment is tailored to your individual pattern.

Regular follow-up with a gastroenterologist (a doctor who specializes in digestive diseases) is important. You will have periodic colonoscopies to monitor the colon and check for complications. People with ulcerative colitis have a slightly higher risk of colon cancer, so screening is part of long-term care.

Many people find that identifying personal triggers—certain foods, stress, or lack of sleep—helps them manage flares. Keeping a symptom diary can reveal patterns. Support groups, whether in person or online, connect you with others managing the same condition and can provide practical tips and emotional support.

Frequently Asked Questions

Is ulcerative colitis the same as irritable bowel syndrome?

No. Irritable bowel syndrome (IBS) causes abdominal pain and changes in bowel habits but does not cause inflammation or ulcers. Ulcerative colitis is an inflammatory disease with visible damage to the colon lining. A colonoscopy can distinguish between them because it shows inflammation and ulcers in ulcerative colitis but a normal colon in IBS.

Can ulcerative colitis go away on its own?

Ulcerative colitis is a chronic condition and does not go away permanently. However, symptoms can go into remission for long periods with or without medication. Some people have one flare and then years without symptoms. Others need ongoing medication to stay in remission. The goal of treatment is to achieve and maintain remission.

What foods should I avoid if I have ulcerative colitis?

There is no single diet that works for everyone. Common trigger foods include high-fiber foods, dairy, spicy foods, and foods high in fat, but triggers vary by person. Keeping a food diary during flares helps identify your personal triggers. During remission, you may tolerate a wider range of foods. A dietitian who works with people with inflammatory bowel disease can help you plan meals.

Can I have children if I have ulcerative colitis?

Yes. Most people with ulcerative colitis can have children. Some medications are safe during pregnancy and breastfeeding, while others need to be paused. Talk with your gastroenterologist and obstetrician before trying to conceive so they can adjust your treatment plan if needed. Pregnancy itself does not worsen ulcerative colitis in most people.

What is the difference between a flare and remission?

Remission is a period with no symptoms or minimal symptoms. A flare is when symptoms return or worsen—you have increased diarrhea, bleeding, cramping, or urgency. Flares can last days to weeks. The goal of treatment is to end a flare and then maintain remission as long as possible through ongoing medication.