Ulcerative Colitis vs Diverticulitis: How to Tell the Difference

The names sound similar, the symptoms can overlap, and when your gut is already causing more than enough uncertainty, the last thing you need is more confusion.

I'm often asked about this difference. Sometimes it’s from people newly diagnosed with Ulcerative Colitis (UC), sometimes from those who’ve lived with Inflammatory Bowel Disease (IBD) for years and suddenly experience a new kind of pain that doesn’t feel familiar. Others have been told they “might” have diverticulitis and are left wondering whether it changes everything they thought they knew about their gut.

What makes this tricky is that both conditions affect the colon, both can cause abdominal pain and bowel changes, and both can sound alarming when you first hear the diagnosis. But beneath the surface, Ulcerative Colitis and diverticulitis are very different conditions, with different causes, different patterns, and very different treatment approaches.

In this blog, I want to gently you through the key differences between Ulcerative Colitis and diverticulitis, why they’re often confused, and how doctors tell them apart. My hope is that by the end, things feel less murky and more manageable, because when it comes to gut health, knowledge can be a form of self-care.

A Quick Overview: What’s the Difference at a Glance?

Before we dive into symptoms, scans, and medical terminology, it can help to zoom out for a moment and look at the big picture.

Although Ulcerative Colitis and diverticulitis both affect the colon, they come from very different processes in the body.

Ulcerative Colitis is a chronic inflammatory condition and part of the broader group of conditions known as Inflammatory Bowel Disease (IBD). It involves ongoing immune-driven inflammation in the lining of the colon. For most people, it follows a pattern of flares and remission and requires long-term management, even when symptoms are well controlled.

Diverticulitis, on the other hand, is usually an acute condition. It develops when small pouches in the wall of the colon (called diverticula) become inflamed or infected. Many people have these pouches without ever knowing it, and diverticulitis tends to appear suddenly, often making people feel quite unwell over a short period of time.

At a glance, the key difference is this:Ulcerative Colitis reflects ongoing inflammation driven by the immune system, while diverticulitis is typically a short-term inflammatory or infectious episode affecting specific areas of the colon.

In the next sections, we’ll unpack each condition properly, what’s happening inside the gut, how symptoms tend to show up, and how doctors distinguish between the two, so you can understand not just what they are, but why they behave so differently in the body.

If you’re still finding your footing with UC terminology and what it all means, my beginner-friendly guide offers a calm, straightforward place to start.

What Is Ulcerative Colitis?

Ulcerative Colitis (often shortened to UC) is a form of Inflammatory Bowel Disease (IBD). It’s a chronic condition, which means it doesn’t come and go once and then disappear. Instead, it tends to move through phases, periods of active inflammation (flares) and periods where symptoms settle (remission).

At its core, Ulcerative Colitis involves ongoing inflammation in the lining of the colon. This inflammation is driven by the immune system and starts in the rectum, spreading upward through the colon in a continuous pattern. How far it extends and how active it is can vary widely from person to person.

Ulcerative Colitis as an Inflammatory Bowel Disease (IBD)

In UC, the immune system mistakenly targets the gut lining, triggering inflammation where there shouldn’t be any. Over time, this inflammation can make the lining of the colon fragile, ulcerated, and more reactive.

One of the important things to understand is that UC isn’t caused by something you ate, stress alone, or an infection you picked up. While diet, stress, and lifestyle can influence symptoms and flares, they aren’t the root cause. That distinction matters, especially when comparing UC to diverticulitis, which often is linked to structural changes in the colon.

Because UC is inflammatory and immune-mediated, treatment usually focuses on calming inflammation, supporting the gut lining, and helping the immune system settle rather than react.

Common Ulcerative Colitis Symptoms

Symptoms of Ulcerative Colitis can look very different depending on how active the inflammation is and how much of the colon is affected. Some people experience mild, nagging symptoms that build slowly, while others notice more intense changes over a shorter period.

Common symptoms include:

• Frequent or urgent bowel movements

• Diarrhoea, sometimes with blood or mucus

• Abdominal cramping or discomfort

• Fatigue that doesn’t improve with rest

• A general sense that the gut feels “unsettled” or unpredictable

  
  

It’s also worth noting that UC doesn’t always stay neatly in the gut. Joint pain, skin changes, and low energy can show up too, especially during active inflammation.

How Ulcerative Colitis Is Diagnosed

Diagnosing Ulcerative Colitis isn’t based on symptoms alone. Because gut symptoms can overlap across many conditions, doctors look for patterns of inflammation and confirmation at a tissue level.

Diagnosis usually involves:

• Colonoscopy with biopsies, which allows doctors to see inflammation and examine tissue under a microscope

• Fecal calprotectin tests, which help measure inflammation in the gut

• Blood tests to check for inflammation and nutrient deficiencies

  
  

This combination helps confirm that inflammation is ongoing and immune-driven, rather than the result of a short-term infection or structural issue, a key distinction when comparing UC with diverticulitis.

For a clear medical overview of how Ulcerative Colitis develops and how it’s diagnosed, the Mayo Clinic offers a helpful, patient-friendly summary you can explore here.

Next, we’ll look at diverticulitis, how it develops, and why it behaves very differently in the body, even though it affects the same part of the gut.

What Is Diverticulitis?

Diverticulitis can sound intimidating, especially when it’s mentioned alongside conditions like Ulcerative Colitis. But while both affect the colon, what’s happening inside the gut is quite different.

Diverticulitis develops from a condition called diverticulosis, which refers to small pouches (diverticula) that form in the wall of the colon. These pouches are very common, especially as we get older, and most people with diverticulosis have no symptoms at all and may never know they have them.

Diverticulitis occurs when one or more of these pouches become inflamed or infected. When that happens, symptoms tend to come on more suddenly and can make people feel acutely unwell.

From Diverticulosis to Diverticulitis

Diverticulosis itself isn’t a disease in the same way Ulcerative Colitis is. It’s a structural change in the colon wall. Over time, pressure inside the colon can cause weak spots to bulge outward, forming small pockets.

Most of the time, these pouches sit quietly and cause no trouble. Diverticulitis develops when one of them becomes irritated, inflamed, or infected, often due to trapped stool or changes in gut motility. This is why diverticulitis is usually described as an episode rather than a long-term inflammatory condition.

Unlike Ulcerative Colitis, diverticulitis does not involve continuous inflammation of the colon lining, and it isn’t driven by an autoimmune process.

If you’d like a deeper explanation of diverticulosis and how it can progress to diverticulitis, the Mayo Clinic breaks this down clearly here.

Common Diverticulitis Symptoms

Diverticulitis symptoms often feel different to those of UC, particularly in how suddenly they appear.

Common symptoms include:

• Sudden, localised abdominal pain (most often on the lower left side)

• Fever or chills

• Nausea or vomiting

• Bloating or tenderness in the abdomen

• Changes in bowel habits, such as constipation or diarrhoea

  
  

Many people describe diverticulitis pain as sharp, persistent, and difficult to ignore. Unlike UC symptoms, which can ebb and flow, diverticulitis often reaches a peak quickly and feels more like an acute illness.

How Diverticulitis Is Diagnosed

Because diverticulitis is usually acute, diagnosis often happens during a flare-up rather than over time.

Doctors typically rely on:

• CT scans, which can clearly show inflamed or infected diverticula

• Blood tests to check for infection and inflammation

• A review of symptoms and physical tenderness

  
  

Colonoscopy is usually avoided during an active diverticulitis episode because the colon wall may be fragile. It may be recommended later, once inflammation has settled, to assess the colon more safely.

Understanding how diverticulitis develops and presents helps explain why it’s treated so differently from Ulcerative Colitis, and why telling the two apart is so important. In the next section, we’ll look at the key differences side by side, to make those distinctions even clearer.

Ulcerative Colitis vs Diverticulitis: Key Differences Explained Clearly

This is the part many people wish someone had explained to them early on. When symptoms overlap, it’s easy to assume everything happening in your gut must fall under the same diagnosis. But Ulcerative Colitis and diverticulitis behave very differently once you understand what’s driving each condition.

Let’s break it down in a way that actually makes sense.

Chronic Inflammation vs Acute Episodes

Ulcerative Colitis is a chronic inflammatory disease. That means inflammation is part of the condition itself, even during quieter phases. Symptoms may ease during remission, but the underlying tendency toward inflammation remains and needs ongoing management.

Diverticulitis is usually acute. It appears suddenly, causes noticeable illness, and then (with appropriate treatment) often resolves. Many people may have one episode in their lifetime and never experience it again.

Immune-Driven vs Structural and Infectious

In UC, the immune system is misfiring. It mistakenly attacks the lining of the colon, creating inflammation where there shouldn’t be any. This is why Ulcerative Colitis sits under the umbrella of Inflammatory Bowel Disease (IBD).

Diverticulitis isn’t driven by immune dysfunction in the same way. It develops when small pouches in the colon wall become inflamed or infected. The issue is more structural and mechanical, rather than autoimmune.

Continuous Inflammation vs Localised Pain

Ulcerative Colitis causes continuous inflammation that starts at the rectum and moves upward through the colon. Symptoms tend to be widespread and related to bowel function as a whole.

Diverticulitis usually affects specific, localised areas of the colon. Pain is often sharply focused, most commonly on the lower left side, and may feel very different from the cramping or urgency associated with UC.

Long-Term Management vs Short-Term Treatment

Because UC is ongoing, treatment focuses on long-term inflammation control, maintaining remission, and protecting the gut lining over time.

Diverticulitis treatment is often short-term, aiming to calm the acute episode. This may include antibiotics, bowel rest, and temporary dietary changes until inflammation settles.

Why Symptoms Alone Can Be Misleading

This is where confusion often creeps in. Abdominal pain, bowel changes, and fatigue can show up in both conditions. But the pattern, speed of onset, and how symptoms respond to treatment usually tell a clearer story than symptoms in isolation.

That’s why doctors rely on imaging, scopes, and lab tests rather than guesswork, and why a new or unfamiliar type of pain is always worth investigating rather than assuming it’s “just my UC.”

Next, we’ll look at a question that often causes anxiety for people with IBD: is it possible to have both Ulcerative Colitis and diverticular disease, and how would you know?

Can You Have Both Ulcerative Colitis and Diverticular Disease?

This question comes up often, especially when symptoms suddenly feel unfamiliar.

The short answer is yes, it’s possible, but it isn’t common. Having Ulcerative Colitis does not automatically mean you’ll develop diverticulitis.

Diverticulosis (the presence of diverticula) becomes more common with age and can exist without causing symptoms. Someone with UC may also have diverticula, but that doesn’t mean those pouches will become inflamed or infected.

What matters most is that UC and diverticulitis behave differently, and doctors are careful not to assume that all gut symptoms fall under one diagnosis.

How Doctors Tell the Difference

When someone with UC experiences new or unusual symptoms, clinicians look at:

• How suddenly symptoms appeared

• Whether pain is localised or more widespread

• Signs of infection, such as fever

• Imaging results, especially CT scans

  
  

A UC flare tends to follow a familiar inflammatory pattern in the lining of the colon. Diverticulitis usually shows up as a localised area of inflammation or infection on imaging.

If something feels different from your usual UC pattern, it’s reasonable to get it checked.

Why Getting the Right Diagnosis Matters

Ulcerative Colitis and diverticulitis may sound similar, but they require very different treatment approaches.

UC management focuses on calming inflammation over the long term and supporting remission. Diverticulitis treatment is usually short-term, aimed at settling an acute episode so the colon can heal.

When the two are confused:

• Treatment may be ineffective

• Recovery can take longer

• Anxiety increases because symptoms don’t improve as expected

  
  

This is why doctors rely on scans, scopes, and inflammatory markers rather than symptoms alone. It’s not about dismissing how you feel; it’s about making sure the response matches what’s actually happening in your gut.

Clear diagnosis brings clarity, and clarity reduces fear. It helps you understand what your body needs right now, rather than guessing or pushing through uncertainty.

What To Do If You’re Unsure What You’re Dealing With

When gut symptoms change, it’s easy to second-guess yourself, especially if you already live with Ulcerative Colitis. But not every new sensation needs to be pushed through or explained away.

If pain feels sharper, more localised, or comes on suddenly, it’s worth checking in with your doctor.

Fever, chills, or feeling acutely unwell are also signs that something different may be happening and should be assessed sooner rather than later.

Doctors don’t expect you to diagnose yourself. What helps is noticing patterns and sharing what feels new or unfamiliar compared to your usual baseline. Imaging, blood tests, and stool markers can quickly clarify whether symptoms point to a UC flare, diverticulitis, or something else entirely.

Seeking clarity isn’t a failure to cope. It’s a way of protecting your gut, your energy, and your peace of mind, and it often leads to faster, more appropriate treatment.

Conclusion

Ulcerative Colitis and diverticulitis may sound similar, but they come from very different processes in the body. Understanding that difference helps you respond appropriately when symptoms change, rather than assuming everything fits under one diagnosis.

Clarity doesn’t mean obsessing over symptoms or jumping to conclusions. It means knowing when something feels familiar, when it doesn’t, and trusting yourself enough to ask for answers. With the right information and support, even confusing gut symptoms can feel more manageable and less overwhelming.

Frequently Asked Questions

Can diverticulitis turn into Ulcerative Colitis?

No. Diverticulitis does not cause Ulcerative Colitis, and UC does not develop from diverticular disease.

Does Ulcerative Colitis increase the risk of diverticulitis?

Not directly. While both affect the colon, they have different causes. It’s possible to have both, but it’s uncommon.

Is blood in stool more common with UC or diverticulitis?

Blood in the stool is more typical of Ulcerative Colitis. Diverticulitis is more often associated with pain and fever.

How do doctors tell a UC flare from diverticulitis?

They look at symptom patterns, blood markers, stool tests, and imaging such as CT scans rather than relying on symptoms alone.

Should I assume new pain is just my UC?

No. If pain feels sudden, sharp, or different from your usual pattern, it’s worth getting checked.