Pain along the side of your abdomen during a bowel movement usually comes from the colon itself, which runs in a roughly rectangular loop from your lower right side, across your upper abdomen, and down your left side. The location of the pain often points toward the cause: left-sided pain is more common because the descending and sigmoid portions of the colon do much of the heavy lifting during defecation. But pain on either side can also come from muscles, nerves, pelvic floor tension, or organs that sit near the colon and get jostled when you bear down. Understanding which structures are involved, and when the pain signals something that needs a doctor’s attention, can help you decide whether this is a nuisance or a red flag.
Why the Left Side Hurts More Often
The left side of your abdomen houses the descending colon and the sigmoid colon, the stretch of bowel where stool firms up and waits before you have a bowel movement. When stool is hard, dry, or bulky, the muscular walls of this segment have to squeeze harder, and that extra effort can produce a cramping or aching pain in the left lower quadrant. This is also the region most vulnerable to diverticulitis, a condition in which small pouches that form in the colon wall become inflamed or infected. Diverticulitis typically causes steady, tender pain in the left lower abdomen, and bowel movements tend to make it worse because the inflamed segment is being asked to contract. Fever and changes in bowel habits often accompany it.
In Western populations, diverticulitis overwhelmingly affects the sigmoid and descending colon.1PubMed. Emergency medicine updates: Acute diverticulitis That anatomical preference is why the phrase “left-sided abdominal pain” shows up so frequently in descriptions of the condition. If you notice sharp left-side pain that gets worse during or right after pooping, especially if you have a low-grade fever, this is one of the first possibilities your doctor will investigate.
When the Right Side Hurts Instead
Right-sided pain during defecation is less common but not rare. The ascending colon climbs up the right side of your abdomen, and it can cramp when moving a large or gas-filled stool load. In some people, diverticulitis can appear on the right side as well, particularly in Asian populations, where right-sided diverticula are more common than in Western countries.
Bearing down also temporarily raises the pressure inside your abdomen, which can press on structures that happen to be inflamed for reasons unrelated to the colon. An ovarian cyst, an inflamed appendix, or a kidney stone sitting in the right ureter can all produce pain that flares when you strain. If right-side pain during bowel movements is new, persistent, or getting worse, it deserves a closer look to rule out these non-colon causes.
Irritable Bowel Syndrome and Oversensitive Nerves
For many people who feel side pain with bowel movements but have no obvious structural problem, irritable bowel syndrome is the most common explanation. IBS is defined by abdominal pain or discomfort linked to changes in bowel patterns, and it remains one of the most frequently diagnosed functional gastrointestinal conditions.2PubMed Central. Managing irritable bowel syndrome The word “functional” means imaging and lab tests look normal; the problem lies in how the gut’s nerves process signals.
A core feature of IBS is visceral hypersensitivity, in which the nerves lining the intestinal wall overreact to normal sensations like stretching, gas, or the passage of stool. This process involves a long list of nerve receptors and chemical messengers, and it can operate both at the gut level and higher up in the brain’s pain-processing circuits.3PubMed Central. The Role of Visceral Hypersensitivity in Irritable Bowel Syndrome: Pharmacological Targets and Novel Treatments The practical result is that a bowel movement that would be painless for someone else produces genuine, sometimes severe, cramping or stabbing pain in the side of the abdomen. The pain often improves after the stool passes, which is one of the hallmarks doctors use to distinguish IBS from other conditions.
If you have been told you have IBS and you experience side pain mainly around bowel movements, that heightened nerve sensitivity is likely the explanation. It does not mean the pain is imaginary; the nerves are actually firing more aggressively than they should.
Inflammatory Bowel Disease
Crohn’s disease and ulcerative colitis, the two main forms of inflammatory bowel disease, can cause flank or side pain during defecation for a different reason than IBS. In IBD, the gut wall itself is inflamed. Inflammatory molecules sensitize the nerve endings in and around the intestine, lowering the threshold at which movement or stretching registers as painful.4PubMed Central. Abdominal Pain in Inflammatory Bowel Disease: An Evidence-Based, Multidisciplinary Review When stool moves through an inflamed segment, it triggers pain that can feel sharp, burning, or crampy along the side where the active disease sits.
One frustrating wrinkle: some people with IBD continue to have pain during bowel movements even when they are told they are in remission. Research suggests that low-grade inflammation can persist beneath what standard tests detect, keeping nerves sensitized.4PubMed Central. Abdominal Pain in Inflammatory Bowel Disease: An Evidence-Based, Multidisciplinary Review If you have IBD and the pain during pooping never fully goes away between flares, that lingering inflammation may be the reason, and it is worth discussing with your gastroenterologist.
Pelvic Floor Tension and Muscle Pain
The muscles of the pelvic floor are supposed to relax when you have a bowel movement, allowing the stool to pass without resistance. When those muscles are chronically tight or go into spasm instead of relaxing, every attempt to poop turns into a battle. The strain radiates outward from the pelvis into the lower abdomen and sides. This condition, sometimes called pelvic floor myofascial pain, is strongly linked to a specific pattern of constipation called rectal evacuation disorder, where the exit mechanism itself is the bottleneck.
Constipated patients with pelvic floor myofascial pain show higher resting muscle tone and tend to paradoxically tighten the muscles they should be relaxing during a bowel movement.5PubMed. Clinical presentation and characteristics of pelvic floor myofascial pain in patients presenting with constipation The result is more straining, more abdominal pressure, and more pain radiating into the flanks. Biofeedback therapy, which teaches you to retrain those muscles, is often an effective treatment and something many people never hear about.
Endometriosis and Painful Defecation
For people with uteruses, endometriosis is an underrecognized cause of pain during bowel movements. Endometriosis involves tissue similar to the uterine lining growing in places it should not be, and when that tissue attaches to or near the bowel, vagina, or bladder, defecation can become genuinely painful. The pain often follows a cyclical pattern tied to menstruation, but it can also be constant.
Research into deeply infiltrating endometriosis has found that painful defecation during menstruation is more frequent when the disease involves the vaginal wall, and chronic pelvic pain is more common when it involves the bowel directly.6PubMed. Relation between pain symptoms and the anatomic location of deep infiltrating endometriosis Gastrointestinal symptoms such as bloating, diarrhea, or constipation often accompany the pain, which is why endometriosis is sometimes misdiagnosed as IBS for years before the real cause is found. If your side pain during bowel movements worsens around your period, endometriosis belongs on the list of possibilities to discuss with a gynecologist.
Abdominal Adhesions and Scar Tissue
If you have had abdominal or pelvic surgery, or if you have a history of conditions that cause internal inflammation, you may have adhesions. These are bands of scar tissue that form between organs and the abdominal wall, essentially gluing structures together that are normally free to slide past each other. When the colon contracts during a bowel movement, adhesions can tug on nearby tissue, producing a pulling or sharp pain in the side.
Adhesions are a common consequence of surgery, radiation, and inflammatory processes, and in some patients they cause chronic symptoms including abdominal pain, bloating, and abnormal bowel patterns that can be daily, intermittent, or episodic.7Annals of Medicine and Surgery. Abdominal adhesions: A practical review of an often overlooked entity Because adhesions do not show up well on standard imaging, they are easy to miss. If you had surgery years ago and now have side pain during bowel movements that no one can explain, adhesive disease is worth considering.
Nerve Entrapment in the Abdominal Wall
Sometimes the pain is not coming from inside the abdomen at all. Anterior cutaneous nerve entrapment syndrome, or ACNES, occurs when one of the small nerves that runs through the abdominal wall muscles gets pinched or compressed. It produces a sharp, localized pain that can feel like it is coming from deep inside but is actually originating in the muscle layers. Straining during a bowel movement tenses those muscles and can make the pinched nerve flare.
ACNES frequently comes with visceral-seeming symptoms that mislead doctors. In one study, about half of patients with the condition also reported altered defecation, along with bloating and nausea.8PubMed Central. Visceral symptoms in patients with anterior cutaneous nerve entrapment syndrome (ACNES): expression of viscerosomatic reflexes? The combination of abdominal pain plus bowel changes naturally leads clinicians to look inside the gut, while the real problem sits in the abdominal wall itself. A simple bedside test, pressing on the tender spot while the patient tenses their abdominal muscles, can help distinguish ACNES from internal causes. If the pain gets worse with muscle tension rather than better, it is likely the wall, not the bowel.
Medications That Mimic Bowel Disease
If you take nonsteroidal anti-inflammatory drugs regularly, whether for arthritis, headaches, or chronic pain, they can damage the lining of the colon in ways that cause pain during bowel movements. NSAID-induced colopathy involves inflammation, ulceration, and sometimes stricture formation in the colon, and it can present with abdominal pain, altered bowel habits, and blood in the stool.9PubMed Central. Non-steroidal anti-inflammatory drug-induced colopathy The symptoms can closely mimic colon cancer or inflammatory bowel disease, which means it sometimes triggers an extensive and anxiety-inducing workup before the medication is identified as the culprit.
Opioid painkillers are another common offender, though through a different mechanism. They slow the colon dramatically, leading to hard, compacted stools that require forceful contractions to move. The resulting cramps and straining can produce pain on either side. If your side pain started after beginning a new medication, that timing is worth mentioning to your doctor.
Ischemic Colitis
Ischemic colitis happens when blood flow to a section of the colon is temporarily reduced, causing tissue damage and inflammation. It typically causes sudden crampy pain on the left side, followed by an urge to defecate and sometimes bloody diarrhea. While most people associate reduced blood flow with older adults who have heart disease, ischemic colitis can also appear in younger people due to different risk factors such as dehydration, certain medications, or clotting disorders.10PubMed Central. Ischemic colitis
Most cases resolve with supportive care, but roughly one in five patients requires surgery, and surgical cases carry high rates of complications.10PubMed Central. Ischemic colitis If you experience sudden severe side pain with bloody or maroon-colored stools, that combination warrants prompt medical evaluation.
How Posture and Straining Make Things Worse
The position you sit in on the toilet affects how much pressure your body generates during a bowel movement, and more pressure means more opportunity for pain. In a standard seated position, the angle between your rectum and anal canal creates a bend that requires your muscles to push harder. Research comparing toilet postures has found that squatting straightens the rectal canal to roughly 100 to 110 degrees, reducing the strain needed to evacuate.11PubMed Central. Sitting vs. squatting: a scoping review of toilet postures and associated health outcomes This is the basic principle behind footstools marketed for bathroom use: elevating your feet while sitting mimics some of the squatting angle and can reduce how hard you have to push.
The trade-off is worth knowing about, though. Squatting also increases pressure inside the abdomen, which can worsen certain conditions like pelvic organ prolapse.11PubMed Central. Sitting vs. squatting: a scoping review of toilet postures and associated health outcomes For someone whose side pain is caused by straining against a tight pelvic floor, a raised-foot position may help. For someone whose pain comes from high intra-abdominal pressure pushing on an inflamed organ, it could make things worse. There is no single “correct” toilet posture; it depends on what is causing the pain.
When Side Pain During Bowel Movements Needs Urgent Attention
Most side pain during pooping is uncomfortable but not dangerous. Gas cramps, mild constipation, and muscle tension account for a large share of cases and tend to come and go without causing harm. But certain patterns warrant a trip to the doctor or emergency room sooner rather than later:
- Blood in the stool: Bright red blood, dark tarry stools, or maroon-colored stool can indicate anything from hemorrhoids to ischemic colitis to colon cancer. Any new rectal bleeding deserves evaluation.
- Fever with abdominal pain: Pain accompanied by a temperature above 100.4°F (38°C) raises concern for diverticulitis, an abscess, or another infectious or inflammatory process.
- Sudden severe pain: A sharp, new onset of intense pain in the side, especially if it does not let up after the bowel movement, can signal a perforation, obstruction, or vascular emergency like ischemic colitis.
- Unintended weight loss: Pain during defecation combined with losing weight without trying can be a sign of IBD, colon cancer, or another condition that needs investigation.
- Pain that wakes you up: IBS pain rarely disrupts sleep. Pain that rouses you from sleep is more likely to have a structural or inflammatory cause that needs imaging or endoscopy.
- Progressive worsening: Pain that has been present for weeks and is steadily getting worse, rather than fluctuating, suggests something is changing inside and should not be ignored.
If none of these red flags apply but the pain keeps recurring, keeping a brief log of when it happens, which side, what your stool looked like, and what you ate can give your doctor useful information. Many of the conditions discussed here overlap in their symptoms, and the pattern of the pain over time often matters more than a single episode.
Constipation as the Quiet Amplifier
Whatever the underlying cause, constipation tends to make side pain during bowel movements worse. Hard stools require stronger colonic contractions, longer straining, and higher abdominal pressures, all of which amplify pain from any source, whether that source is a nerve, inflamed bowel, adhesion, or tight pelvic floor. Research on severe chronic constipation has shown significant links between slow stool transit through the colon and the severity of symptoms, including pain.12American Journal of Gastroenterology. Symptoms and physiology in severe chronic constipation
Addressing constipation does not always fix the underlying problem, but it frequently reduces how much the underlying problem hurts. Adequate fluid intake, fiber from food rather than supplements when possible, and physical activity all help keep stool soft and transit times reasonable. For people with pelvic floor dysfunction, adding fiber alone sometimes makes things worse because the increased bulk runs into the same exit problem. In those cases, working with a pelvic floor physical therapist to address the muscle coordination issue is usually more effective than piling on more fiber.