What Is Ulcerative Colitis? A Nurse Explains the Basics

By Anna Curran, RN, BSN, PHN · Last reviewed October 2026

What is ulcerative colitis? Ulcerative colitis (UC) is a long-term inflammatory bowel disease that causes swelling and sores (ulcers) on the inner lining of the large intestine. It usually starts in the rectum and can spread up the colon in one unbroken stretch. Symptoms tend to come and go, with flares and calmer times called remission.

If you or someone you love was just diagnosed, it is normal to feel overwhelmed. Here is a clear look at what UC is, how it differs from other gut problems and what the future can look like.

What Is Ulcerative Colitis and What Happens in Your Colon

Your large intestine, or colon, is the last part of your digestive tract. It absorbs water and forms stool before it leaves through the rectum.

In UC, the immune system reacts in an abnormal way and attacks the inner lining of the colon. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains that this causes inflammation and ulcers. The inflamed lining can bleed and make mucus, and it has a hard time absorbing water. That is why bloody diarrhea is such a common sign.

UC is a chronic condition. That means it does not go away on its own, but it can be well controlled with treatment. Many people go long stretches with few or no symptoms.

How Ulcerative Colitis Differs From Crohn’s Disease and IBS

UC is often confused with two other conditions. Knowing the difference can help you understand your care.

Ulcerative colitis vs. Crohn’s disease

UC and Crohn’s disease are the two main types of inflammatory bowel disease (IBD). They share many symptoms, but they behave differently. Mayo Clinic describes these key differences:

Location: UC affects only the colon and rectum. Crohn’s can show up anywhere from the mouth to the anus.
Pattern: UC inflammation is continuous. It starts at the rectum and spreads upward with no healthy gaps. Crohn’s often skips areas, leaving healthy patches between inflamed spots.
Depth: UC stays in the innermost lining of the colon. Crohn’s can go through the full thickness of the bowel wall, which can lead to narrowing, tunnels called fistulas and pockets of infection.

You can learn more in our guide to what Crohn’s disease is.

Ulcerative colitis vs. IBS

Irritable bowel syndrome (IBS) is a different condition. It can cause belly pain, bloating, diarrhea or constipation. But IBS does not cause inflammation or damage to the digestive tract.

UC does cause inflammation, ulcers and bleeding. This difference matters because the treatments are very different. Blood in your stool is not a typical IBS symptom and always needs a doctor’s attention.

Types of Ulcerative Colitis

Doctors group UC by how much of the colon is inflamed. The Crohn’s & Colitis Foundation and Cleveland Clinic describe these main types:

Type	Where the inflammation is	Common symptoms
Ulcerative proctitis	Only the rectum	Rectal bleeding, rectal pain, urgency
Proctosigmoiditis	Rectum and the sigmoid colon (the lower S-shaped part)	Bloody diarrhea, cramps, urgency
Left-sided colitis	From the rectum up the left side of the colon	Bloody diarrhea, left-sided belly pain, weight loss
Extensive colitis (pancolitis)	Most or all of the colon	Bloody diarrhea that can be severe, belly pain, weight loss, low appetite

Mayo Clinic notes that with proctitis, rectal bleeding may be the only sign. Some people with proctitis even have constipation.

The type you have helps guide treatment. For example, medicine given into the rectum may work well when only the lower colon is affected. The extent of UC can also change over time.

Who Gets Ulcerative Colitis?

According to NIDDK, about 600,000 to 900,000 people in the United States have UC. It can start at any age, but it most often begins between ages 15 and 30. Mayo Clinic notes it can also start after age 60.

You may be more likely to get UC if:

A parent, brother, sister or child has IBD
You are of Jewish descent, especially Ashkenazi Jewish
You are white, though UC occurs in people of all races and backgrounds

What Causes It?

Doctors are not sure what causes UC. NIDDK lists several factors that likely work together:

Genes: UC sometimes runs in families.
Immune reactions: The immune system reacts abnormally and inflames the colon.
Gut bacteria: People with IBD have differences in their gut microbes. Researchers are still studying how this connects.
Environment: Outside factors may play a role, but this is still being studied.

NIDDK notes that researchers have not found that specific foods cause UC. Some foods may make symptoms worse, but you did nothing to cause this.

Common Symptoms

Symptoms depend on how much of the colon is inflamed and how active the disease is. The most common include:

Diarrhea, often with blood, mucus or pus
Belly cramps and pain
A sudden, urgent need to have a bowel movement
Feeling like you need to go even when your bowel is empty
Fatigue, fever and weight loss with more severe disease

For a full list and warning signs, see our guide to ulcerative colitis symptoms and flares.

Possible Complications

Most people with UC never have serious complications, but it helps to know what to watch for. NIDDK and Mayo Clinic list these:

Anemia from blood loss
Bone loss (osteoporosis), sometimes linked to steroid use
Problems outside the gut, such as swelling in the joints, skin, eyes and liver
Blood clots
Slow growth in children
Severe bleeding or dehydration
Toxic megacolon, a rare but life-threatening swelling of the colon
Perforation, a hole in the colon wall

Call 911 or go to the emergency room if you have severe belly pain, a swollen or hard belly, heavy rectal bleeding, a high fever, a racing heart or signs of severe dehydration such as dizziness or very little urine.

Ulcerative Colitis and Colon Cancer Screening

Long-term inflammation raises the risk of colon cancer. NIDDK explains that the risk is higher when:

More of the colon is involved
The disease is more severe
UC started at a younger age
You have had UC for a longer time
You also have a liver condition called primary sclerosing cholangitis (PSC)
Someone in your family has had colon cancer

Proctitis alone carries the least risk, according to the Crohn’s & Colitis Foundation and Cleveland Clinic.

The good news is that screening works. NIDDK says doctors usually recommend a colonoscopy every 1 to 3 years, starting 8 years after UC began. If you also have PSC, colonoscopies are usually done every year starting at diagnosis. Your gastroenterologist will set the right schedule for you. Keep these appointments, even when you feel well.

How Ulcerative Colitis Is Treated

The goal of treatment is to calm inflammation, ease symptoms and keep you in remission for the long term. Most people use medicine. Options range from mesalamine for mild to moderate UC to biologics and pills that target the immune system for moderate to severe UC.

Some people need surgery to remove the colon and rectum. Cleveland Clinic explains this is the only “cure” for UC, since the disease only affects the colon. Read more in our guide to ulcerative colitis treatment.

Food also plays a supporting role. See our ulcerative colitis diet guide for practical tips.

What Is the Outlook?

UC is a lifelong condition, but most people live full, active lives. Cleveland Clinic notes that about half of people with UC have mild symptoms during flares. Remission can last weeks or even years.

Cleveland Clinic reports that in up to 30% of people, symptoms get worse over time and surgery is eventually needed. With today’s wider range of medicines, more people have choices if their first treatment does not work.

Staying in touch with your care team, taking your medicine as prescribed and keeping up with colonoscopies are some of the best things you can do for your future health.

Frequently Asked Questions

Is ulcerative colitis the same as Crohn’s disease?

No. Both are types of IBD, but UC only affects the colon and rectum, and the inflammation is continuous. Crohn’s can affect any part of the digestive tract and often skips areas.

Can ulcerative colitis be cured?

There is no medicine that cures UC, but treatment can control it and keep you in remission. Surgery to remove the colon and rectum is considered a cure, because UC only affects the colon.

Is ulcerative colitis caused by stress or diet?

There is no proof that diet causes UC, though some foods can make symptoms worse. Doctors believe it comes from a mix of genes, immune reactions, gut bacteria and environment.

Does ulcerative colitis mean I will get colon cancer?

No. Most people with UC never get colon cancer. Your risk is higher than average, so regular colonoscopies are important to find and remove changes early.

The Bottom Line

Ulcerative colitis is a chronic inflammatory bowel disease that causes ulcers in the lining of the colon and rectum. It differs from Crohn’s disease by staying in the colon in one continuous stretch, and from IBS by causing real inflammation and bleeding. Most people manage UC well with treatment and live full lives. Keep up with your care team and colonoscopies, and get emergency care for severe pain, heavy bleeding or a high fever.