Right flank pain, the area between your lower ribs and hip on the right side of your back, most commonly comes from kidney stones, muscle strains, or kidney infections. But because several organs sit near or behind the right flank, the list of possible causes is longer than most people expect. The type of pain you feel, how it started, and what other symptoms accompany it can narrow things down considerably.
Kidney Stones
Kidney stones are the single most common reason people develop sudden, intense flank pain. They affect roughly 1 in 11 Americans, and while men over 50 have a higher overall prevalence (9.8% compared to 7.7% in women), the gap disappears in adults under 50, where rates are essentially equal between sexes. Obesity, high sodium intake, and a history of pregnancy all increase the risk.
The pain from a kidney stone is distinctive. It typically hits as a serious, sharp pain in the side and back below the ribs, then spreads to the lower abdomen and groin as the stone moves through the urinary tract. Rather than staying constant, the pain comes in waves that vary in intensity. You may also notice a burning sensation when urinating, pink or red urine, or a persistent urge to urinate even when your bladder isn’t full. The location and severity of the pain can shift as the stone travels, which sometimes confuses people into thinking the problem has changed.
When a stone is suspected, the standard first imaging study is a CT scan of the abdomen and pelvis without contrast dye. This scan has a sensitivity as high as 97% for detecting stones and is considered the reference standard by the American College of Radiology. If results are inconclusive, an MRI or contrast-enhanced CT may follow.
Kidney Infection (Pyelonephritis)
A kidney infection is a urinary tract infection that has traveled upward from the bladder into one or both kidneys. When it affects the right kidney, it produces right flank pain that’s often accompanied by fever, chills, nausea, and painful urination. The hallmark finding is tenderness at the costovertebral angle, the spot where your lowest ribs meet your spine. This tenderness can range from mild to severe and is typically noticeable even with gentle pressure on the area.
Visible blood in the urine shows up in 30 to 40% of pyelonephritis cases in women, particularly younger women. However, up to 30% of patients can have normal-looking urine tests even when the infection is significant, so a clean dipstick alone doesn’t rule it out. Kidney infections are treated with antibiotics and, if caught early, usually resolve without complications. Left untreated, though, they can progress to abscess formation or a dangerous bloodstream infection.
Muscle Strains and Musculoskeletal Causes
Not every flank pain points to an internal organ. Musculoskeletal flank pain is common and feels noticeably different from kidney-related pain. It presents as a dull ache rather than sharp, wave-like pain, and it worsens with specific movements, twisting, or pressing on the area. Back muscles that have been pulled or strained can radiate pain outward into the flank, which sometimes leads people to worry about a kidney problem when the real issue is mechanical.
This is especially common in people who are active in sports, lift weights, or do physical labor. The treatment is straightforward: rest, over-the-counter pain relief, and gradual return to activity. If the pain doesn’t improve within a week or two, or if it came on without any obvious physical cause, further evaluation makes sense.
Appendicitis in an Unusual Position
Most people associate appendicitis with pain in the lower right abdomen, and that’s the classic presentation. But in some people, the appendix curves upward and sits behind the large intestine, a position called retrocecal. When the appendix is in this location and becomes inflamed, the pain can show up in the right flank instead, mimicking a kidney problem. Studies of retrocecal appendicitis have found that this atypical pain pattern often delays diagnosis because it doesn’t match the textbook picture. The key clue is that the pain tends to worsen steadily over hours, often accompanied by loss of appetite, nausea, and a low-grade fever that gradually climbs.
Shingles (Before the Rash Appears)
Shingles can produce flank pain that’s genuinely puzzling because the pain often arrives 1 to 5 days before any rash becomes visible. During this prodromal stage, you may feel tingling, burning, or sharp pain along a band on one side of your body, including the flank. The skin in that area may look slightly flushed. Because there’s no rash yet, this pain frequently gets attributed to a muscle strain or kidney issue until the characteristic blistering rash finally appears along the same strip of skin. Shingles pain is almost always one-sided, which is the defining feature that eventually points to the correct diagnosis.
Right Flank Pain During Pregnancy
Pregnant women experience right flank pain more often than left, and the reasons are partly anatomical. Mild hydronephrosis, a backup of urine that causes the kidney to swell, is reported in up to 90% of pregnant women. It happens because the growing uterus compresses the ureters (the tubes connecting kidneys to the bladder), and pregnancy hormones relax the smooth muscle walls of those tubes, slowing urine flow.
The right side is disproportionately affected because the uterus naturally tilts slightly to the right as it grows, while the sigmoid colon on the left side offers some protection to the left ureter. This swelling is usually harmless and resolves after delivery, but it can occasionally lead to kidney infection or, rarely, a serious systemic infection. Pregnant women who had more than twice the odds of developing kidney stones compared to women who had never been pregnant, so stone-related flank pain is also worth considering during pregnancy.
Liver and Gallbladder Problems
The liver and gallbladder sit in the upper right portion of the abdomen, and inflammation in either organ can produce pain that wraps around toward the right flank. Gallbladder attacks from gallstones typically cause pain that starts under the right ribcage after eating a fatty meal and may radiate to the right flank or between the shoulder blades. The pain often builds to a peak over 15 to 30 minutes and can last several hours. Liver conditions, including hepatitis or abscess, tend to produce a deeper, more constant ache in the same region. These causes are usually distinguishable from kidney pain because they’re more closely tied to eating, tend to sit higher, and don’t produce urinary symptoms.
How the Type of Pain Points to the Cause
The character of your pain is one of the most useful clues for figuring out what’s behind it:
- Sharp, wave-like pain that radiates to the groin suggests a kidney stone.
- Steady pain with fever and painful urination points toward a kidney infection.
- Dull ache that worsens with movement or pressure is typically musculoskeletal.
- Burning or tingling in a band-like pattern on one side may be early shingles.
- Pain that started vaguely and has been worsening for hours, with nausea and low appetite, raises concern for appendicitis.
- Pain after eating, especially fatty foods, with discomfort under the right ribs, suggests gallbladder involvement.
Flank pain that comes with high fever, blood in the urine, inability to keep fluids down, or pain so severe you can’t find a comfortable position warrants prompt medical evaluation. The same is true for pain that develops suddenly and doesn’t let up, or flank pain accompanied by a rapid heart rate and lightheadedness, which can signal infection spreading beyond the kidney or another urgent cause.