Why can a kidney infection cause pain in the loins or flanks?

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The most common cause of urinary tract infection is invasion into the urethra of Escherichia coli, a type of bacterium that normally inhabits the bowel. — urinary tract infection The most common cause of urinary tract infection is invasion into the urethra of *Escherichia coli*, a type of bacterium that normally inhabits the bowel.

A kidney infection, known medically as pyelonephritis, causes pain in the loins or flanks primarily due to the inflammation of the kidney tissue and the renal pelvis.1

During an acute infection, the lining of the renal structures—specifically the renal pelvis and the calyces—becomes inflamed. This inflammatory process, which can also involve the formation of abscesses within the kidney tissue, leads to localized tenderness and pain or aches that are typically felt in the lower back and flank regions.1