The most common bowel problems are constipation, hemorrhoids, irritable bowel syndrome (IBS), diarrheal infections, and diverticular disease. Less common but still widespread conditions include inflammatory bowel disease (IBD), celiac disease, and bacterial overgrowth in the small intestine. Most of these affect tens of millions of people in the U.S. alone, and many overlap in their symptoms, which can make them tricky to tell apart without a proper evaluation.
Chronic Constipation
Constipation affects roughly 63 million Americans and is one of the most frequent reasons people seek help for digestive issues. It’s defined not just by how often you go but by the consistency of your stool. On the Bristol Stool Scale, a widely used clinical tool, constipation shows up as Type 1 (separate hard lumps) or Type 2 (sausage-shaped but lumpy). Anything firmer than a smooth, soft log suggests your colon is absorbing too much water from waste before it passes.
Common causes include low fiber intake, not drinking enough fluids, lack of physical activity, and certain medications like opioids, iron supplements, and some antidepressants. For many people, adding fiber gradually (aiming for 25 to 30 grams per day), staying hydrated, and moving more resolves the problem within a few weeks. When it doesn’t, over-the-counter options like osmotic laxatives can help by drawing water into the intestine. Constipation that persists for months or arrives suddenly with no clear explanation deserves a closer look from a doctor.
Hemorrhoids
About 75 percent of people over 45 develop hemorrhoids at some point. These are swollen blood vessels in and around the lower rectum and anus, and they come in two forms. Internal hemorrhoids sit higher up inside the rectum and are graded on a scale of one to four based on whether they stay in place or bulge outward. At grade one, they’re invisible and painless. By grade three or four, they protrude and may need to be pushed back in manually, or can’t be pushed back at all.
External hemorrhoids sit under the skin around the anus. They’re generally more noticeable because they can become painful, especially if a blood clot forms inside them. The hallmark symptom of internal hemorrhoids is bright red blood on toilet paper or in the bowl, usually painless. Itching, swelling, and discomfort during sitting are more typical of external ones. Straining during bowel movements, sitting on the toilet for long periods, and chronic constipation or diarrhea all increase risk. Warm sitz baths, high-fiber diets, and topical treatments handle most cases without any procedures.
Irritable Bowel Syndrome (IBS)
IBS affects over 15 million Americans and is the most common functional bowel disorder, meaning the gut looks structurally normal but doesn’t work the way it should. A formal diagnosis requires recurrent abdominal pain averaging at least one day per week over the past three months, combined with at least two of the following: pain related to bowel movements, a change in how often you go, or a change in how your stool looks. Symptoms must have started at least six months before the diagnosis is made.
IBS comes in subtypes. Some people deal primarily with diarrhea, others with constipation, and many alternate between both. Bloating, gas, and cramping are nearly universal. Stress, certain foods, hormonal shifts, and disrupted sleep can all trigger flare-ups. There’s no single test for IBS. Doctors typically diagnose it after ruling out other conditions like celiac disease or IBD.
Diet is the first-line treatment for most people. A low-FODMAP diet, which temporarily eliminates certain fermentable carbohydrates found in foods like onions, garlic, wheat, and some fruits, has shown meaningful results in clinical trials. Across multiple randomized controlled studies, between 50 and 80 percent of patients following a low-FODMAP plan met responder criteria, defined as a significant reduction in symptom severity scores. That said, the diet is meant to be a short-term elimination phase followed by gradual reintroduction, not a permanent restriction. Working with a dietitian helps ensure you’re not cutting out nutrients unnecessarily.
Diverticular Disease
Diverticulosis is the condition of having small pouches, called diverticula, that form in weak spots along the intestinal wall. It’s extremely common after age 40 and often causes no symptoms at all. Many people discover they have it incidentally during a colonoscopy or imaging scan done for another reason.
The trouble starts when bacteria multiply inside one of those pouches and cause inflammation or infection. That’s diverticulitis, and it announces itself with sharp pain (usually in the lower left abdomen), fever, nausea, and sometimes changes in bowel habits. Mild cases often resolve with a short course of antibiotics and a temporary liquid or low-fiber diet. Severe or recurrent episodes can lead to complications like abscesses or narrowing of the intestine, which may require more involved treatment. A high-fiber diet is generally recommended to reduce the risk of new pouches forming and to keep existing ones from becoming inflamed.
Inflammatory Bowel Disease (IBD)
IBD is an umbrella term for two chronic conditions: ulcerative colitis and Crohn’s disease. Both involve the immune system attacking the digestive tract, but they differ in important ways.
Ulcerative colitis is limited to the large intestine. It starts in the rectum and spreads upward in a continuous line with no gaps, and the inflammation stays in the innermost lining of the colon. Symptoms include bloody diarrhea, urgency, and cramping. Crohn’s disease can strike anywhere from the mouth to the anus, often in patches with healthy tissue in between. The inflammation can extend through the full thickness of the intestinal wall, which is why Crohn’s carries a higher risk of complications like fistulas (abnormal tunnels between tissues) and abscesses.
Both conditions follow a relapsing-remitting pattern, meaning symptoms flare up and then quiet down, sometimes for months or years. Weight loss, fatigue, and poor nutrient absorption are common during active disease. Treatment focuses on controlling inflammation and preventing flares, typically with medications that calm the immune response. Many people with IBD live full, active lives between flares, but the condition requires ongoing monitoring.
Celiac Disease
Celiac disease is an autoimmune condition triggered by gluten, a protein found in wheat, barley, and rye. When someone with celiac eats gluten, their immune system damages the lining of the small intestine, impairing its ability to absorb nutrients. Symptoms range from diarrhea, bloating, and abdominal pain to less obvious signs like fatigue, iron-deficiency anemia, bone loss, and skin rashes.
Diagnosis starts with a blood test that looks for specific antibodies the body produces in response to gluten. This test is highly accurate, with sensitivity as high as 100 percent in some studies, but there’s one important catch: you need to be eating gluten regularly for the results to be reliable. If blood work is positive, a biopsy of the small intestine during an upper endoscopy confirms the diagnosis by showing characteristic damage to the intestinal lining. The only effective treatment is a strict, lifelong gluten-free diet. Most people see significant improvement within weeks to months of eliminating gluten, though full intestinal healing can take longer.
Bacterial Overgrowth in the Small Intestine
Small intestinal bacterial overgrowth, often called SIBO, occurs when bacteria that normally live in the large intestine colonize the small intestine in excessive numbers. The most common symptom is diarrhea, often accompanied by bloating, gas, and abdominal pain. In more severe cases, the overgrown bacteria interfere with nutrient absorption, leading to weight loss and nutritional deficiencies.
SIBO is more common in people with conditions that slow intestinal movement, such as diabetes, prior abdominal surgery, or certain connective tissue disorders. Diagnosis has historically relied on breath tests that measure hydrogen or methane gas after drinking a sugar solution, but these tests have significant limitations. The lactulose breath test, for example, largely measures how fast food moves through your gut rather than where bacteria are located, and its accuracy is poor. Treatment typically involves a course of targeted antibiotics, and addressing the underlying cause is important to prevent recurrence.
Symptoms That Need Prompt Attention
Many bowel problems share overlapping symptoms, and most turn out to be benign. But certain signs warrant a prompt evaluation because they can indicate colorectal cancer or other serious conditions. These include rectal bleeding or blood in the stool, unexplained weight loss, persistent changes in bowel habits (new constipation or diarrhea that doesn’t resolve), excessive fatigue that isn’t explained by other factors, and ongoing abdominal pain or cramping. A constant feeling that you need to have a bowel movement when you don’t is another signal worth reporting. These symptoms don’t automatically mean something serious, but they do need to be investigated rather than waited out.