Diverticulosis means you have small bulging pouches (called diverticula) in the wall of your colon. Diverticulitis means one or more of those pouches has become inflamed or infected. The difference is essentially quiet versus angry: diverticulosis is the structural condition, and diverticulitis is what happens when something goes wrong with it. Most people with diverticulosis never develop diverticulitis, but understanding both helps you know what to watch for.
How Common Diverticulosis Really Is
Diverticulosis is one of the most common findings on a colonoscopy, especially as people age. About 5% of adults have diverticula by age 40, roughly 50% by age 60, and up to 65 to 70% by age 80. In most cases, these pouches cause no symptoms at all and are discovered incidentally during imaging or screening procedures. You can live your entire life with diverticulosis and never know it.
Of those who do have diverticulosis, only a fraction go on to develop diverticulitis. And among those who develop diverticulitis, about 12% experience a complicated case involving an abscess, perforation, or other serious problem. So while the underlying condition is extremely common, the serious version of it is not.
What Causes the Pouches to Form
Diverticula develop at weak spots in the colon wall, typically where blood vessels pass through the muscle layer. Over time, pressure inside the colon pushes the inner lining outward through these weak points, creating small balloon-like sacs. A low-fiber diet, which leads to smaller and harder stools requiring more pressure to move, is one of the most well-established contributing factors. Age-related changes in the colon wall also play a role, which is why diverticulosis becomes so much more common with each decade of life.
How Diverticulitis Develops
The leading explanation for why a quiet pouch becomes inflamed involves a small blockage. A piece of hardened stool (sometimes called a fecalith) gets trapped inside a diverticulum, irritating the lining. This causes swelling, congestion, and further obstruction of the pouch. In some cases, the trapped material leads to tiny tears in the pouch wall, allowing bacteria to leak into surrounding tissue. That bacterial spread is what turns localized irritation into a full infection.
Symptoms That Set Them Apart
Diverticulosis typically causes no symptoms. Some people experience mild cramping or bloating, but many feel nothing at all. There is no fever, no tenderness, and no signs of infection. It is a structural finding, not an illness.
Diverticulitis, on the other hand, announces itself clearly. The hallmark symptom is steady, persistent pain in the lower left side of the abdomen. Unlike gas pain or a cramp that comes and goes, this pain tends to be constant and may worsen over hours or days. Fever is common, though usually below 102°F. Other symptoms can include nausea, loss of appetite, constipation or diarrhea, and abdominal bloating or distension.
The location of the pain is a strong diagnostic clue. Tenderness isolated to the left lower abdomen makes diverticulitis roughly 10 times more likely than other causes. A doctor may also feel a firm mass in that area if the inflammation has created swelling or an abscess.
How Diverticulitis Is Diagnosed
If your doctor suspects diverticulitis based on your symptoms and a physical exam, a CT scan is the standard way to confirm it. The scan reveals telltale signs: thickening of the colon wall (healthy walls are thin, while inflamed walls can swell well beyond their normal thickness), haziness or streaking in the fat surrounding the colon, and sometimes small pockets of air or fluid outside the bowel that indicate a microperforation or abscess.
Blood work also helps. About 55% of people with acute diverticulitis show elevated white blood cell counts, a sign the immune system is fighting infection. A blood marker called C-reactive protein, which rises with inflammation, can further support the diagnosis. When left-sided tenderness is combined with a high C-reactive protein level and no vomiting, the likelihood of diverticulitis increases dramatically.
Treating Uncomplicated Diverticulitis
Most cases of diverticulitis are uncomplicated, meaning the inflammation hasn’t led to an abscess, perforation, or other structural damage. Treatment focuses on letting the colon rest and heal. During the acute phase, a clear liquid diet is typically recommended, with gradual return to solid foods as symptoms improve. Most people feel significantly better within a few days.
One of the bigger shifts in treatment over the past decade involves antibiotics. They were once considered mandatory for every case of diverticulitis, but current guidelines from the American Gastroenterological Association now recommend using them selectively rather than routinely for mild, uncomplicated cases in otherwise healthy people. Antibiotics are still advised when someone has other health conditions, a weakened immune system, symptoms that aren’t improving, high inflammatory markers, or signs of a fluid collection or longer stretch of inflamed bowel on the CT scan.
When Diverticulitis Becomes Complicated
About 12% of diverticulitis cases involve complications. These include abscesses (walled-off pockets of infection near the colon), perforation (a hole in the colon wall that allows contents to leak into the abdominal cavity), bowel obstruction, and fistulas (abnormal tunnels that form between the colon and a neighboring organ like the bladder or another part of the intestine). Fistulas account for roughly 14% of these complications.
Warning signs that diverticulitis may be complicated include a rapid heart rate, dropping blood pressure, severe or worsening pain, and high fever. Small abscesses can sometimes be drained with a needle guided by imaging. Larger abscesses, perforations, or fistulas often require surgery to remove the damaged section of colon. About 10% of people who develop complicated diverticulitis need additional procedures beyond the initial treatment.
Living With Diverticulosis
Since diverticulosis itself isn’t a disease that needs treatment, managing it is really about reducing the chance it progresses to diverticulitis. The most consistent recommendation is eating a high-fiber diet. Adults should aim for about 14 grams of fiber per 1,000 calories consumed, which works out to roughly 28 grams per day on a standard 2,000-calorie diet. Good sources include fruits, vegetables, whole grains, beans, and nuts.
And yes, nuts are on that list. For years, people with diverticulosis were told to avoid nuts, seeds, and popcorn based on the theory that small particles could lodge in a pouch and trigger inflammation. That advice has been thoroughly debunked. There is no evidence that these foods cause diverticulitis, and many high-fiber foods that help protect the colon (like nuts and seeds) were unnecessarily off-limits for decades. Current guidance from the Mayo Clinic specifically lists nuts as part of a healthy, high-fiber diet for people with diverticula.