Diverticulitis is inflammation or infection of small pouches that form in the wall of your colon. These pouches, called diverticula, are extremely common and usually harmless on their own. But when one or more of them becomes inflamed, the result is pain (typically in the lower left abdomen), fever, and digestive upset that can range from mild and manageable at home to severe enough to require emergency surgery.
About 10% to 25% of people who have these pouches will eventually develop diverticulitis. The condition is strongly tied to age: fewer than 20% of people have diverticula by age 40, but roughly 60% have them by age 60. That said, up to 20% of diverticulitis cases occur in people younger than 50.
How Diverticula Form and Why They Get Inflamed
Diverticula develop where the inner lining of the colon pushes outward through weak spots in the muscular wall, usually right next to small blood vessels. A low-fiber diet is one of the main contributors. Without enough fiber, stool tends to be smaller and harder, which forces the colon to generate more pressure to move things along. Over time, that repeated pressure causes the lining to bulge outward.
Having diverticula (a condition called diverticulosis) is not the same as having diverticulitis. Most people with diverticulosis never develop symptoms. Diverticulitis happens when a pouch becomes blocked, often by a small piece of stool. That blockage can irritate the lining, reduce blood flow to the area, and allow bacteria that normally live in the colon to cross the damaged wall. The result is an inflammatory cascade that can lead to swelling, infection, and in serious cases, a hole in the colon wall.
Shifts in gut bacteria also play a role. People who develop diverticulitis tend to have fewer beneficial bacteria that produce short-chain fatty acids, which help maintain the colon’s protective lining. When that barrier weakens, the colon becomes more vulnerable to inflammation.
What Diverticulitis Feels Like
The hallmark symptom is pain in the lower left side of the abdomen, reported by about 70% of patients. The pain is usually crampy and can last for days. It often gets worse with movement or pressure on the area and may ease temporarily after passing gas or having a bowel movement.
Other common symptoms include fever, nausea, vomiting, bloating, flatulence, and a noticeable change in bowel habits. Some people become constipated, while others experience looser stools. A mild case might feel like persistent abdominal soreness with low-grade fever. A severe episode can bring sharp, constant pain, high fever, and an inability to keep food down.
How It’s Diagnosed
A CT scan is the standard tool for confirming diverticulitis, and it is remarkably accurate. Studies using thin-slice CT with contrast material report sensitivity and specificity both around 99%. The scan shows the hallmark signs: thickening of the colon wall (visible in about 96% of cases), inflammation in the surrounding fat (95%), and the diverticula themselves (91%). It also reveals complications like abscesses, free air from a perforation, or fluid buildup, which helps determine how aggressively the episode needs to be treated.
Treatment for Uncomplicated Cases
Most episodes of diverticulitis are uncomplicated, meaning there’s no abscess, perforation, or other structural damage. For otherwise healthy people with mild symptoms, the American Gastroenterological Association now recommends that antibiotics be used selectively rather than routinely. Many mild flares resolve with rest and dietary changes alone. Antibiotics are still advised when symptoms are more severe, when blood tests show significant inflammation, when imaging reveals a fluid collection or a longer stretch of inflamed colon, or when the patient has other health conditions or a weakened immune system.
During a flare, the typical approach starts with a clear liquid diet for a few days: broths, pulp-free juices, and water. As pain and symptoms improve, you gradually shift to low-fiber foods like cooked or canned fruits and vegetables without skins or seeds, along with small amounts of protein spread across five or six small meals per day. Raw fruits and vegetables are avoided during this phase to give the colon time to heal. Once the flare has fully resolved, fiber is slowly reintroduced over several weeks.
Complications That Require More Aggressive Care
Complicated diverticulitis involves structural damage beyond simple inflammation. The most common complication is an abscess, a walled-off pocket of infection near the inflamed pouch. Smaller abscesses can sometimes be drained with a needle guided by imaging, while larger ones may need surgical drainage.
A perforation occurs when the inflamed pouch ruptures, allowing bacteria and stool to leak into the abdominal cavity. This causes peritonitis, a life-threatening infection of the abdominal lining that requires emergency surgery. Warning signs include sudden, severe abdominal pain, a rigid abdomen, high fever, and rapid heart rate.
Fistulas are another potential complication. These are abnormal tunnels that form between the colon and a nearby organ, most commonly the bladder. Symptoms can include air or stool in the urine or recurrent urinary tract infections. Fistulas generally require elective surgery to repair.
Repeated episodes of inflammation can also cause scarring that narrows the colon, leading to partial or complete bowel obstruction. Symptoms include worsening constipation, abdominal distension, and cramping.
When Surgery Becomes Necessary
Surgery is not needed for a first episode of uncomplicated diverticulitis or for diverticula that aren’t causing symptoms. Emergency surgery is reserved for specific situations: a perforated colon with signs of peritonitis, worsening infection despite treatment, or significant bleeding that can’t be controlled by other means.
Elective surgery, planned in advance and performed when the colon isn’t actively inflamed, is considered for people who develop fistulas, significant narrowing of the colon, or recurrent episodes that meaningfully reduce quality of life. The decision is individualized. Older guidelines recommended surgery after a set number of flares, but current practice focuses more on the severity of symptoms and how much they affect daily life.
Reducing the Risk of Recurrence
Recurrence is less common than many people expect. In a study of over 3,100 patients hospitalized for diverticulitis, only 13.3% had another episode within nine years. Several lifestyle factors influence that risk.
Regular physical activity, a high-fiber diet, and maintaining a healthy weight are the strongest protective factors. Vegetarian diets are associated with lower risk, while high meat consumption increases it. Nuts and corn, once thought to trigger flares, are actually linked to reduced risk and do not need to be avoided. Smoking increases the chance of recurrence, as does regular use of NSAIDs (like ibuprofen) and opioid pain medications.
For people who also have high blood pressure, calcium channel blockers may offer a dual benefit. These medications reduce the pressure inside the colon by relaxing smooth muscle, and some evidence suggests they lower recurrence rates. Long-term preventive antibiotics, on the other hand, have not shown clear benefit and are generally not recommended.