Stones are formed when some dissolved substances in normal urine are precipitated for various reasons and are retained in the kidney and continue to grow. Most kidney stones occur in middle-aged and older people, more in men than in women. Kidney stones may persist for a long time without symptoms, especially in larger stones. Smaller stones have a large range of motion, and when small stones enter the pelvic ureteral junction or ureter, they cause violent peristalsis of the ureter to urge the stones out, and colic and hematuria occur. The pain caused by kidney stones can be classified as dull pain or colic. 40-50% of patients have a history of intermittent episodes of pain. The pain is often located in the lower back and abdomen, mostly paroxysmal, but can be constant. Some of the pains may only manifest as back pain and discomfort, but activity or labor may cause the pain to flare up or worsen. The pain often radiates to the lower abdomen, groin or inner femur, or to the labia in women. During an attack of renal colic, the patient looks acutely ill, curled up in bed, with both hands pressing on the abdomen or waist, or even rolling over in bed, moaning and groaning. The attack often lasts for several hours, but may be relieved in a few minutes. When the renal colic is severe, the face is pale, the whole body has cold sweat, the pulse is thin and rapid, and even the blood pressure drops, showing a state of deficiency, accompanied by nausea, vomiting, abdominal distension and constipation. During the attack of colic, the urine volume decreases, and after the colic is relieved, there may be polyuria. Hematuria is another major symptom of kidney stones. When pain is present, it is often accompanied by flesh-eye hematuria or microscopic hematuria, the latter being the most common. Large amounts of flesh-eye hematuria are not uncommon, and the hematuria may worsen after physical activity. Patients with kidney stones may excrete sand and stones in the urine, especially during episodes of pain and hematuria, with sand particles or small stones mixed in the urine. Obstruction or stabbing pain occurs when stones pass through the urethra. The common complications of kidney stones are obstruction and infection, and many cases seek medical attention for symptoms of urinary tract infection. Obstruction can cause hydronephrosis and a mass in the upper abdomen or lower back.