The hallmark symptom of diverticulitis is abdominal pain, most often in the lower left side, that comes on suddenly and feels intense. Beyond that signature pain, you may also experience fever, nausea, and changes in bowel habits. The specific combination and severity of symptoms depends on whether the inflammation is mild or complicated, acute or chronic, and where in the colon it occurs.
Where the Pain Shows Up
Diverticulitis happens when small pouches in the colon wall become inflamed or infected. Because these pouches most commonly form in the lower left portion of the colon (the sigmoid colon), most people feel pain in the lower left abdomen. That pain can also spread into the pelvis or radiate to the lower back.
The location isn’t universal, though. In people of Asian descent, the pouches more commonly develop in the first part of the colon, which sits in the upper right abdomen. Diverticulitis in that location causes upper abdominal pain and can look a lot like appendicitis, gallbladder problems, or other right-sided conditions. Right-sided diverticulitis tends to cause pain that’s more diffuse and located slightly higher and more to the outside than appendicitis pain would be.
How the Pain Feels
The pain can follow different patterns. In an acute attack, it often arrives suddenly and feels sharp or intense from the start. In other cases, it begins as a mild ache and worsens over several days, building gradually as inflammation increases. Some people notice the intensity fluctuating, easing for a stretch before ramping back up. During a flare, pressing on the affected area typically makes the pain worse, and so can moving, coughing, or straining.
Digestive Symptoms
Alongside the pain, diverticulitis commonly disrupts normal digestion. You may notice:
- Nausea or vomiting: More common in left-sided disease than right-sided cases, where nausea tends to be less frequent.
- Changes in bowel habits: Both constipation and diarrhea can occur during a flare. Interestingly, the long-held assumption that constipation causes diverticular disease has been challenged. Large studies have found that people who have more than one bowel movement per day actually have a 30% higher risk of developing diverticulitis compared to those with daily bowel movements. People with less frequent bowel movements had a lower risk. So constipation during a flare is a symptom of the inflammation itself, not necessarily the underlying cause.
- Bloating and gas: Inflammation in the colon wall can slow digestion locally and trap gas, creating a sense of pressure or fullness.
- Loss of appetite: Many people simply don’t feel like eating during an active episode, especially when nausea is present.
Fever and Signs of Infection
A low-grade fever is common with diverticulitis and signals that your body is fighting inflammation or infection in the colon wall. When the inflammation is mild (uncomplicated diverticulitis), the fever tends to stay modest. Higher fevers, chills, or a rapid heart rate suggest the infection may be more serious, potentially involving an abscess (a walled-off pocket of pus) or a perforation where the inflamed pouch has developed a hole.
Blood tests during a diverticulitis episode typically show elevated white blood cell counts and higher levels of inflammatory markers. While you won’t see these numbers yourself, they help explain why you feel generally unwell, fatigued, or “off” even beyond the abdominal symptoms.
Acute vs. Chronic Symptoms
A single acute episode is the most recognizable form: sudden pain, fever, and digestive symptoms that develop over hours to a couple of days. Most people recover within a week or two with rest and, in some cases, antibiotics.
Chronic diverticulitis is different. If you’ve had repeated bouts, especially ones that cluster within a short window, this is sometimes called “smoldering” diverticulitis. Think of it like the embers of a fire that never fully goes out. Rather than dramatic flares, you may deal with ongoing low-level abdominal pain, intermittent cramping, irregular bowel habits, and a general sense that your digestion never quite returns to normal between episodes. The symptoms are less intense than an acute attack but more persistent, and they can significantly affect quality of life.
Right-Sided Diverticulitis
Right-sided diverticulitis deserves separate mention because it mimics appendicitis closely enough to fool even experienced clinicians. The pain settles in the lower right abdomen, and it typically affects younger adults (ages 20 to 40) compared to classical left-sided diverticulitis, which peaks later in life. A few differences can help distinguish it from appendicitis: the pain tends to last longer before someone seeks medical care (anywhere from one to 14 days compared to the rapid escalation of appendicitis), nausea and vomiting are less common, and fever is less frequent. The abdomen is also less likely to feel rigid or extremely tender to the touch. That said, imaging is usually needed to tell the two apart definitively.
Warning Signs of Complications
Most diverticulitis episodes are uncomplicated and resolve without surgery. But roughly 12% of cases involve complications that need more aggressive treatment. Symptoms that signal something more serious include:
- Severe, worsening pain that spreads across the entire abdomen: This can indicate perforation, where the inflamed pouch has ruptured and is leaking contents into the abdominal cavity.
- A rigid, board-like abdomen: The abdominal muscles tighten involuntarily when the lining of the abdominal cavity becomes inflamed, a condition called peritonitis.
- High fever with chills: Suggests a significant infection, possibly an abscess that may need drainage.
- Inability to pass gas or have a bowel movement: Repeated inflammation can cause scarring that narrows the colon, potentially leading to a blockage.
- Blood in the stool: While diverticular bleeding is technically a separate condition from diverticulitis, the two can overlap. Significant rectal bleeding during an episode warrants urgent evaluation.
People with weakened immune systems are more likely to develop severe or complicated diverticulitis and may not show the typical warning signs as clearly, since their immune response is blunted. In these cases, imaging is especially important even when symptoms seem mild.
What Diverticulitis Can Be Mistaken For
Several other conditions share symptoms with diverticulitis, which is why imaging (usually a CT scan) plays such an important role in diagnosis. Left-sided pain with fever can resemble a urinary tract infection, kidney stones, or gynecological conditions like ovarian cysts or endometriosis. Right-sided cases, as noted, closely mimic appendicitis. Inflammatory bowel disease (Crohn’s disease or ulcerative colitis) and colon cancer can also cause overlapping symptoms like persistent pain, changes in bowel habits, and bleeding. If your symptoms are new, recurring, or don’t fit a clear pattern, imaging and sometimes a later colonoscopy help confirm what’s actually going on.