A diverticulitis flare-up typically feels like a persistent, severe pain in the lower left side of your abdomen that builds over hours and doesn’t go away when you shift positions. The pain is often accompanied by fever, nausea, and a noticeable change in your bowel habits. Most people describe it as a deep, constant ache rather than the sharp, stabbing sensation of something like a pulled muscle, though it can intensify when you move, cough, or press on the area.
Where the Pain Shows Up
The hallmark of a diverticulitis flare is pain concentrated in the lower left abdomen. That’s because the sigmoid colon, the S-shaped section of your large intestine just above the rectum, is where most diverticula (small pouches in the intestinal wall) form and where inflammation most commonly strikes. The pain tends to settle into one spot and stay there, which helps distinguish it from conditions that cause more diffuse or shifting discomfort.
Some people feel it closer to the center of the abdomen at first, with the pain migrating to the left side as inflammation worsens. In rarer cases, particularly in people of Asian descent, pain can appear on the right side because diverticula form in a different part of the colon. The area will often feel tender to the touch, and you may notice your belly feels bloated or distended. Some people can actually feel the swollen section of colon through the abdominal wall.
The Full Range of Symptoms
Pain is the main event, but a flare brings several other symptoms along with it. A low-grade fever is common, reflecting the inflammation and sometimes mild infection happening inside the colon wall. Nausea is frequent, and some people vomit, especially if the inflammation is more severe. Your bowel habits will likely shift: constipation is the more common change, though some people develop sudden diarrhea instead. Rectal bleeding can occur but is less typical of a straightforward flare.
Many people also describe a general feeling of being unwell, similar to the early stages of a stomach flu, but with pain that’s more localized and constant. Eating can make the discomfort worse, and you may lose your appetite entirely for the first day or two.
How It Differs From IBS and Other Conditions
Because abdominal pain, bloating, and bowel changes overlap with so many conditions, it’s worth knowing what sets a diverticulitis flare apart. Irritable bowel syndrome can cause similar symptoms, but IBS pain tends to be more intermittent and is often triggered by specific foods or stress. Diverticulitis pain is more steady and doesn’t fluctuate with dietary triggers in the same way.
Appendicitis is another common concern. Appendicitis pain usually starts around the belly button and moves to the lower right side, while diverticulitis pain settles on the lower left. Appendicitis also tends to escalate more rapidly, over 12 to 24 hours, while a diverticulitis flare can build more gradually. If you’re unsure, the location of the pain is your best initial clue, but imaging is what confirms the diagnosis. A CT scan with contrast is the gold standard, with about 94% sensitivity and 99% specificity for identifying diverticulitis.
What Recovery Looks Like
If your flare is uncomplicated, meaning there’s no abscess, perforation, or other serious complication, you’ll likely manage it at home. Your doctor may recommend starting with clear liquids only for a few days to give your colon a rest. As the pain eases, you’ll gradually transition to low-fiber foods, then slowly reintroduce fiber over several weeks. Most people with a mild flare start feeling noticeably better within two to three days of starting this approach.
One shift in how flares are treated: antibiotics aren’t always necessary for uncomplicated cases. A large clinical trial called DINAMO randomized 480 patients to either antibiotics or pain relievers alone and found no significant difference in hospitalization rates or emergency visits between the two groups. Pain control was actually better in the group that took only over-the-counter pain medication. A meta-analysis of nine studies reached the same conclusion, finding that observation without antibiotics was a viable approach for otherwise healthy patients. Antibiotics are still recommended if you have significant other health conditions, a weakened immune system, or signs of a systemic infection like high fever or rapidly worsening symptoms.
Signs a Flare Is Getting Serious
Most flares resolve without complications, but some progress to something more dangerous. Pay close attention if your pain suddenly intensifies or spreads across your entire abdomen, if your fever climbs above 101°F (38.3°C), or if your abdomen becomes rigid and extremely painful to touch. These can signal a perforation, where the inflamed pouch has burst, or an abscess forming near the colon. Significant rectal bleeding, persistent vomiting, or feeling lightheaded and confused are also red flags that need emergency evaluation.
A CT scan can identify warning signs of complicated diverticulitis, including air bubbles outside the colon wall, fluid collections, or a long segment of inflamed intestine. These findings change the treatment approach significantly and may require hospitalization.
What Triggers a Flare
Having diverticula (small pouches) in your colon wall is extremely common, especially after age 40, and most people with them never develop symptoms. A flare happens when one or more of those pouches becomes inflamed or infected. The exact trigger for any individual episode isn’t always clear, but low dietary fiber, obesity, smoking, and a sedentary lifestyle all increase the risk. Some people notice patterns over time, but unlike IBS, flares don’t respond predictably to removing specific food triggers.
Once you’ve had one flare, your risk of having another is higher, though most people don’t experience frequent recurrences. Building up to a high-fiber diet after recovery, staying physically active, and maintaining a healthy weight are the most evidence-supported strategies for reducing the chance of a repeat episode.