A diverticulitis attack is a sudden episode of inflammation in one or more small pouches (diverticula) that have formed along the wall of your colon. The hallmark symptom is abdominal pain, usually in the lower left side, that can come on suddenly and intensely or start mild and build over hours. About 80% of attacks are uncomplicated, meaning they resolve without serious problems, but some can lead to infections, abscesses, or tears in the colon wall that require urgent treatment.
What Happens Inside Your Colon
Diverticula are small, bulging pockets that push outward through weak spots in the colon wall. Many people develop them with age and never know they’re there. A diverticulitis attack starts when one of these pouches becomes inflamed, often involving a small tear in its lining. That tear can allow bacteria to take hold, leading to a localized infection at the site. It’s not always clear whether the tear or the inflammation comes first, but the result is the same: pain, swelling, and the cascade of symptoms that follow.
What a Diverticulitis Attack Feels Like
The defining symptom is pain in the lower left abdomen. For some people it strikes suddenly and feels intense right away. For others it begins as a dull ache that worsens over a day or two, sometimes fluctuating in intensity. The pain often gets worse when you press on the area.
Beyond the pain, a typical attack can include:
- Fever, often reaching 38°C (100.4°F) or higher
- Nausea, sometimes with vomiting
- Changes in bowel habits, including sudden diarrhea or constipation
- Abdominal tenderness that makes it uncomfortable to move, cough, or be touched
The intensity varies widely. A mild attack might feel like persistent cramping with some tenderness, while a severe one can leave you unable to stand comfortably. If you’ve had one before, you’ll likely recognize the pattern quickly the second time around.
Uncomplicated vs. Complicated Attacks
Doctors divide diverticulitis into two categories, and the distinction matters because it determines how aggressively the attack needs to be treated.
Uncomplicated diverticulitis accounts for roughly 80% of cases. The inflammation is contained to the colon wall and surrounding tissue. There’s no abscess, no perforation, and no blockage. These attacks are uncomfortable but generally manageable at home.
Complicated diverticulitis means the inflammation has caused a secondary problem. That can include an abscess (a walled-off pocket of pus near the colon), a perforation (a hole in the bowel wall that leaks contents into the abdominal cavity), a fistula (an abnormal tunnel that forms between the colon and a neighboring organ like the bladder), or an intestinal obstruction from severe swelling or scarring. These complications can be life-threatening, particularly if a perforation leads to peritonitis, a widespread infection of the abdominal lining.
How an Attack Is Diagnosed
If you go to a doctor or emergency room with suspected diverticulitis, a CT scan is the standard diagnostic tool. On the scan, doctors look for telltale signs: thickening of the colon wall at the inflamed segment, haziness in the fat surrounding the colon (called fat stranding, which signals inflammation spreading beyond the bowel), and the inflamed diverticulum itself. Small bubbles of free air near the colon can indicate a microperforation. If an abscess has formed, it shows up as a fluid-filled mass with a visible wall.
The CT findings also help doctors grade the severity, which guides treatment decisions. A mild attack with just wall thickening and some surrounding inflammation is managed very differently from one with a large abscess or free air throughout the abdomen.
Treatment for a Typical Attack
For uncomplicated diverticulitis, treatment has shifted in recent years. Current guidelines from the American College of Surgeons confirm that carefully selected patients with mild, uncomplicated attacks can recover without antibiotics. This applies to otherwise healthy people without immune system problems or signs of spreading infection. If you do have other health conditions, a weakened immune system, or signs that the infection is worsening, antibiotics remain part of the treatment plan.
Most uncomplicated attacks are treated at home with rest and dietary changes. Your doctor may start you on a clear liquid diet to give the inflamed section of your colon a break. As the pain improves, you gradually transition to low-fiber foods that are easy to digest. Over the following weeks, you slowly reintroduce fiber, eventually working back up to a high-fiber diet that includes fruits, vegetables, and whole grains. This progression matters because jumping back to normal eating too quickly can aggravate the healing tissue.
Complicated attacks are a different situation. Small abscesses can sometimes be drained through the skin using imaging guidance. Larger abscesses, perforations with widespread infection, or a bowel obstruction may require emergency surgery to remove the damaged section of colon. This is uncommon but represents the most serious end of the spectrum.
How Long an Attack Lasts
A mild, uncomplicated attack typically improves within a few days of starting treatment, though full recovery takes longer. Most people feel significantly better within a week, but tenderness and some digestive irregularity can linger for two to three weeks. The dietary progression from liquids back to a full high-fiber diet often takes several weeks on its own, so even after the acute pain is gone you’ll still be in recovery mode.
Complicated attacks take longer. If surgery is needed, recovery can extend to six weeks or more depending on the procedure.
Risk of Another Attack
One of the biggest concerns after a first attack is whether it will happen again. The risk is lower than many people expect. A large study of over 3,100 patients hospitalized for diverticulitis found that only about 13% had a recurrence over nine years of follow-up. That means most people who have one attack won’t have a second one.
A high-fiber diet is the most well-supported strategy for reducing your risk. Fiber softens stool and helps it move through the colon with less pressure, which may prevent existing diverticula from becoming inflamed. If you’re not used to eating much fiber, add it gradually over several weeks to avoid bloating and gas.
Signs That Require Immediate Attention
Most diverticulitis attacks are manageable, but certain symptoms signal a complication that needs emergency care. Heavy rectal bleeding, especially if it’s accompanied by dizziness, confusion, pale or clammy skin, or shortness of breath, requires immediate evaluation. Sudden, severe abdominal pain that worsens rapidly, a high fever that doesn’t respond to treatment, or a rigid abdomen that’s extremely painful to touch can indicate a perforation or peritonitis. These are situations where the bowel wall has been breached and intestinal contents are leaking into the abdominal cavity, which is a surgical emergency.