Lower side pain can stem from dozens of different structures packed into a small region of your body, and the cause ranges from a pulled muscle that heals on its own to a vascular emergency that needs surgery within hours. Your kidneys, ureters, colon, reproductive organs, lower ribs, and several layers of muscle all sit in or near the flank and lower abdomen, so pinpointing the source based on pain alone is genuinely difficult. Understanding what else accompanies the pain, how it started, and who you are (your age, sex, and medical history) narrows the list faster than the location itself.
What Counts as Your “Lower Side”
When people say their lower side hurts, they usually mean the area between the bottom of the ribcage and the hip bone, wrapping from the front of the abdomen around toward the back. Doctors split this zone into overlapping regions: the flank (the back portion, roughly where your kidneys sit), the lower quadrants of the abdomen (left or right), and the iliac fossa (the bony bowl of the pelvis). Pain that starts in one of these areas can radiate into another, which is why a kidney stone may feel like a groin problem and a colon issue may feel like back pain. The side that hurts matters, too. Left-sided lower pain has a different shortlist of likely causes than right-sided lower pain, though several conditions can show up on either side.
Kidney Stones and Urinary Tract Problems
Kidney stones are one of the most recognizable causes of sudden, severe flank pain. The pain typically hits in waves and can radiate from the back down toward the groin or even into the testicle, because the ureter shares nerve pathways with the genitofemoral and ilioinguinal nerves.1PubMed Central. Distal Ureteric Stone Presenting Solely As Testicular Pain: Diagnostic Lessons From a Primary-Care Setting A stone that has moved into the lower ureter often causes pain closer to the front of the lower abdomen rather than the classic back-and-flank location, which can make it feel more like a bowel or gynecological issue. Nausea and vomiting are common companions, and you may notice blood in your urine even if the pain is manageable.
Urinary tract infections can also produce lower side pain, especially when the infection has climbed up to the kidney (pyelonephritis). In that scenario you typically have fever, chills, and painful or frequent urination alongside the flank tenderness.2PubMed Central. Urolithiasis presenting as right flank pain: a case report A simple bladder infection rarely causes side pain on its own, so if you feel genuine flank tenderness along with urinary symptoms, it suggests the infection may involve the kidney and warrants prompt medical attention.
Digestive Causes on the Left Side
If the pain is on your lower left side, diverticulitis is near the top of the list, particularly if you are over 50. Diverticulitis happens when small pouches that form along the colon wall become inflamed or infected. It overwhelmingly favors the left side because the sigmoid colon, where these pouches cluster in Western populations, sits in the left lower abdomen.3PubMed Central. Acute Diverticulitis: A Rare Cause of Abdominal Pain A Case of Acute Diverticulitis The pain is usually steady rather than crampy, worsens with movement or pressing on the area, and often comes with fever and a change in bowel habits. Mild cases respond to antibiotics and a temporary change in diet; complicated cases involving abscess or perforation may need drainage or surgery.
Left lower quadrant pain in older adults has a broad differential that also includes renal colic, urinary infections, gynecological problems, a condition called epiploic appendicitis (where a small fat pad on the colon twists and loses blood supply), and even colon cancer that has perforated.4PubMed. Acute left lower quadrant abdominal pain: ultrasonographic differential diagnosis Epiploic appendicitis deserves a mention because it mimics diverticulitis almost perfectly on physical exam but usually resolves on its own without antibiotics. A CT scan is often the only way to tell them apart.
Digestive Causes on the Right Side
Appendicitis is the classic right-lower-side emergency. It often starts as a vague ache around the belly button that migrates over hours to the right lower quadrant. But appendicitis does not always follow the textbook: in older adults, typical signs like fever, guarding, and pain migration become less reliable, leading to diagnostic delays and higher complication rates.5PubMed Central. Acute appendicitis in geriatric population: a clinical and prognostic comparison of surgical intervention and conservative management That subtlety is one reason appendicitis in people over 65 carries a higher perforation rate than in younger adults.
Inflammation of the ileum, the last portion of the small intestine, also produces right-lower-side pain and is most commonly associated with Crohn’s disease.6PubMed Central. Ileitis: when it is not Crohn’s disease But ileitis can also result from infections, certain medications (particularly NSAIDs), and other inflammatory conditions. If your right-sided pain keeps coming back, especially with diarrhea or unintentional weight loss, it is worth investigating beyond a single episode.
Ovarian and Reproductive Causes
In women and people with ovaries, lower side pain has an additional layer of possibilities. Ovarian cysts are extremely common and usually painless, but they can cause sharp, sudden pain if they rupture or twist (torsion). Torsion tends to produce severe, one-sided lower abdominal pain that starts suddenly and does not let up.7e-CliniC. Ovarian Cyst Torsion: A Case Report It is a surgical emergency because the twisted ovary loses its blood supply, and the window to save the ovary narrows with every hour. Torsion can happen at any age, including in children, and also during pregnancy, where it most often presents in the first trimester.8Journal of Surgical Research and Reviews. Normal Pregnancy Outcome After Emergency Ovarian Cystectomy for Ovarian Cyst Torsion in the First Half of Pregnancy: A Case Report
Ectopic pregnancy is another reproductive emergency that causes lower side pain, usually between weeks four and twelve. The pain is typically one-sided and may come with vaginal bleeding and dizziness. Any person of reproductive age with sudden lower abdominal or flank pain and a missed or late period should have ectopic pregnancy ruled out quickly, because a ruptured ectopic can cause life-threatening internal bleeding.
Mittelschmerz, or ovulation pain, is a far more benign cause. It shows up mid-cycle, alternates sides from month to month, and lasts a few hours to a day. It can feel surprisingly sharp, but it is harmless. The key distinction is that ovulation pain is self-limiting and predictable once you notice the pattern, whereas torsion and ectopic pain escalate and do not resolve on their own.
Musculoskeletal Pain and Slipping Rib Syndrome
Not every lower-side pain comes from an organ. The muscles and ribs in the area are common culprits, especially after heavy lifting, a new exercise routine, or a fall. A strained oblique muscle or psoas muscle can produce a deep, nagging ache along the flank or lower abdomen that worsens when you twist, cough, or bend. The psoas, a deep hip flexor that runs along the lumbar spine, is particularly tricky because pain from it can mimic kidney or intestinal problems.
A less familiar but surprisingly common condition is slipping rib syndrome. The lower ribs (the 8th, 9th, and 10th) are not attached directly to the breastbone; instead, they connect through cartilage that can become loose or hypermobile.9PubMed Central. Treatment of Chronic Pain Due to Slipping Rib Syndrome Using Ultrasound-Guided Intercostal Cryoneurolysis: A Case Report When these ribs shift, they can trap or irritate the intercostal nerve running beneath them, producing a burning or stabbing pain in the lower chest and upper abdomen that can easily be mistaken for a gallbladder, kidney, or cardiac problem.10PubMed Central. A new sign of the slipping rib syndrome? Slipping rib syndrome is widely considered underdiagnosed because clinicians do not always think to check for it, and standard imaging like X-rays and CT scans often looks normal.11Journal of Pulmonology and Intensive Care. Awareness and management of slipping rib syndrome If you have recurring lower chest or upper flank pain that flares with certain movements and has not been explained by organ-based testing, ask your doctor about a “hooking maneuver” test, which physically checks whether a lower rib slips.
When Nerves Are the Problem
Nerve-related pain can produce sensations in the lower side that feel alarmingly like something going wrong with an organ. Shingles (herpes zoster) is the most dramatic example. The virus reactivates along a nerve root and can cause severe, burning pain in a band-like pattern across one side of the torso days before any rash appears. During that pre-rash phase, the pain can mimic an acute abdominal emergency closely enough to send people to the emergency room for surgical evaluation.12PubMed Central. Shingles (Herpes Zoster) Mimicking Acute Abdomen Once the characteristic blistering rash shows up a day or two later, the diagnosis becomes obvious, but the delay can lead to unnecessary imaging or even exploratory surgery in rare cases.
Pinched or irritated nerves from spinal problems (like a herniated disc in the lower thoracic or upper lumbar spine) can also refer pain to the flank or lower abdomen. This type of pain often changes with position, worsens with coughing or straining, and may come with numbness or tingling along a stripe of skin. It can coexist with genuine organ pathology, which complicates diagnosis.
Vascular Emergencies That Mimic Common Problems
Two vascular conditions deserve attention because they can disguise themselves as more routine causes of lower side pain and carry serious consequences if missed.
An abdominal aortic aneurysm (AAA) is a bulging of the body’s largest artery as it passes through the abdomen. When it becomes symptomatic or starts leaking, it often presents with abdominal pain, flank pain, or back pain.13PubMed Central. Abdominal Aortic Aneurysm: An Overlooked Etiology of Low Back Pain The danger is that this pain can closely resemble kidney stones or a musculoskeletal backache. In one documented case, an elderly man with left flank pain turned out to have both a kidney stone and a symptomatic AAA, illustrating how one diagnosis can mask another.14PubMed Central. Point of Care Ultrasound (POCUS) Used to Rapidly Diagnose Both Renal Colic and a Symptomatic Abdominal Aortic Aneurysm in an Elderly Man with Left Flank Pain AAA is most common in men over 65, especially those who smoke or have high blood pressure. If you are in that demographic and develop unexplained flank or back pain, mention the possibility to your doctor.
Ischemic colitis occurs when blood flow to part of the colon drops suddenly, causing crampy lower abdominal pain (usually on the left) followed by bloody diarrhea. It can happen in younger people without traditional cardiovascular risk factors.15PubMed Central. Unexpected presentation of ischemic colitis: a case report and review of the literature The combination of abdominal pain and blood in the stool is the hallmark, and it always warrants urgent evaluation.
Functional and Stress-Related Abdominal Pain
Sometimes lower side pain persists or recurs without any structural cause that tests can identify. Functional abdominal pain and irritable bowel syndrome (IBS) are among the most common diagnoses in both children and adults with chronic or recurrent belly pain. These are real conditions with real pain, not imaginary complaints. They arise from a disordered interaction between the gut and the nervous system, and they are diagnosed based on specific symptom patterns rather than by ruling everything else out.
In children and adolescents especially, recurrent abdominal pain is extremely common and is often functional in nature.16PubMed Central. Functional abdominal pain and irritable bowel syndrome in children and adolescents That does not mean the workup should be skipped. It means that after appropriate testing has excluded structural disease, the focus shifts to management strategies like dietary modification, stress reduction, and sometimes targeted medications. Adults with IBS often describe pain that favors one side, comes and goes with bowel movements, and flares during periods of stress or dietary indiscretion. If this sounds familiar and your tests have come back clean, a conversation about functional pain may be more productive than another round of imaging.
Red Flags That Mean You Should Go Now
Most episodes of lower side pain are not emergencies, but certain combinations of symptoms signal that something dangerous may be happening. Seek emergency care if your lower side pain comes with any of the following:
- Fever above 101°F (38.3°C) with chills: suggests infection that may have spread, such as pyelonephritis, a diverticular abscess, or a perforated appendix.
- Blood in your stool or vomit: raises concern for ischemic colitis, a perforated ulcer, or other conditions that can deteriorate rapidly.
- Sudden, severe pain with lightheadedness or fainting: in women, this pattern can indicate a ruptured ectopic pregnancy or a hemorrhaging ovarian cyst; in anyone, it may signal internal bleeding from a ruptured aneurysm.
- Inability to pass gas or have a bowel movement along with bloating: suggests bowel obstruction, which can become a surgical emergency.
- Pain that started after trauma: even a seemingly minor fall or blow to the side can cause organ injury (spleen, kidney) that bleeds slowly before symptoms worsen.
- A pulsating sensation in the abdomen with back or flank pain: in older adults, this can indicate a symptomatic or leaking aortic aneurysm.
Pain that is severe but not accompanied by these red flags still deserves medical evaluation if it lasts more than a few hours, wakes you from sleep, or prevents you from carrying on normal activity. “Wait and see” is reasonable for mild, self-resolving discomfort, but not for pain that is getting worse over time.
How Doctors Figure Out What Is Wrong
The initial assessment usually involves a physical exam, blood work, and a urine test. From there, imaging is the main tool for sorting through the long list of possibilities. Ultrasound is often the first imaging study because it is fast, widely available, and avoids radiation. It works well for identifying gallstones, kidney stones, ovarian cysts, and aortic aneurysms. For conditions like appendicitis and diverticulitis, however, CT scans are substantially more sensitive. In a head-to-head comparison, CT detected appendicitis with about 94% sensitivity compared to 76% for ultrasound, and detected diverticulitis with about 81% sensitivity compared to 61% for ultrasound.17PubMed Central. A comparison of the Accuracy of Ultrasound and Computed Tomography in common diagnoses causing acute abdominal pain
In practice, the choice often depends on who you are. Children, pregnant women, and young adults are more likely to start with ultrasound to avoid radiation. Older adults with acute pain and concerning symptoms are more likely to go straight to CT because the diagnostic stakes are higher and the conditions in question (diverticulitis, cancer, vascular problems) are harder to see on ultrasound. If the first imaging study is inconclusive and symptoms persist, the next step is usually the other modality or, in some cases, MRI.
Pregnancy and the Elderly Present Differently
Two groups deserve special mention because lower side pain in these populations is both more common and harder to diagnose.
During pregnancy, the expanding uterus shifts organs out of their usual positions, making it harder to localize pain. Conditions like appendicitis, kidney stones, and ovarian torsion all occur during pregnancy, but the symptoms may be attributed to normal pregnancy discomfort, delaying diagnosis. Flank pain during pregnancy can also signal rarer but dangerous conditions: pyelonephritis is more common in pregnant women due to anatomical changes in the urinary tract, and in rare cases, flank pain can indicate spontaneous adrenal hemorrhage, a life-threatening event that requires urgent management.18PubMed Central. Flank pain in the third trimester as a clue to diagnose spontaneous adrenal hemorrhage The bottom line for pregnant individuals: do not dismiss new or worsening side pain as “just pregnancy.” Get it checked.
In older adults, the same principle applies in reverse. Pain perception often dulls with age, and the classic inflammatory signs that clinicians rely on (fever, localized tenderness, muscle guarding) become less pronounced. As a result, serious conditions like appendicitis and diverticulitis can progress further before they are caught, increasing the risk of complications like perforation and abscess.5PubMed Central. Acute appendicitis in geriatric population: a clinical and prognostic comparison of surgical intervention and conservative management Older adults also face unique risks like AAA and ischemic colitis that younger patients rarely have. If you are over 65 and develop persistent side pain, even mild pain, a lower threshold for imaging is warranted.
Post-Surgical and Hernia-Related Pain
If you have had abdominal or flank surgery in the past, your lower side pain may relate to the surgery itself. Incisional hernias can develop months or years after an operation, allowing tissue to bulge through a weak spot in the abdominal wall. Flank hernias in particular are uncommon but can occur after kidney surgery or other retroperitoneal procedures. Repair is usually effective, though some patients develop chronic pain afterward, occasionally requiring removal of mesh material placed during the initial repair.19PubMed. Laparoscopic transperitoneal repair of flank hernias: a retrospective review of 27 patients Adhesions (bands of scar tissue inside the abdomen) are another post-surgical culprit. They can cause intermittent pain, partial bowel obstruction, or both, and they sometimes develop years after the original procedure.
Chronic post-surgical pain is a recognized entity that affects a meaningful fraction of people who undergo abdominal operations. The pain can stem from nerve damage during the procedure, mesh irritation, or ongoing inflammation at the surgical site. It is worth reporting to your surgeon or a pain specialist rather than assuming that post-operative discomfort is just something to live with.